Carleson operators on doubling metric measure spaces

4 Proof of Finitary Carleson

To prove Proposition 2.0.1, we already fixed in Chapter 2 measurable functions \({\sigma _1},\sigma _2, {Q}\) and Borel sets \(F,G\). We have also defined \(S\) to be the smallest integer such that the ranges of \(\sigma _1\) and \(\sigma _2\) are contained in \([-S,S]\) and \(F\) and \(G\) are contained in the ball \(B(o, \frac14 D^S)\).

The proof of the next lemma is done in Section 4.1, following the construction of dyadic cubes in [ .

Lemma 4.0.1 grid existence
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There exists a grid structure \((\mathcal{D}, c,s)\).

The next lemma, which we prove in Section 4.2, should be compared with the construction in [ .

Lemma 4.0.2 tile structure

For a given grid structure \((\mathcal{D}, c,s)\), there exists a tile structure \(({\mathfrak P},{\mathcal{I}},{\Omega },{\mathcal{Q}},{\mathrm{c}},{\mathrm{s}})\).

Choose a grid structure \((\mathcal{D}, c,s)\) with Lemma 4.0.1 and a tile structure for this grid structure \(({\mathfrak P},{\mathcal{I}},{\Omega },{\mathcal{Q}},{\mathrm{c}},{\mathrm{s}})\) with Lemma 4.0.2. Applying Proposition 2.0.2, we obtain a Borel set \(G'\) in \(X\) with \(2\mu (G')\leq \mu (G)\) such that for all Borel functions \(f:X\to {\mathbb {C}}\) with \(|f|\le \mathbf{1}_F\) we have 2.0.22.

Lemma 4.0.3 tile sum operator

We have for all \(x\in G\setminus G'\)

\begin{equation} \label{eq-sump} \sum _{{\mathfrak p}\in {\mathfrak P}}T_{{\mathfrak p}} f(x)= \sum _{s=\sigma _1(x)}^{\sigma _2(x)} \int K_{s}(x,y) f(y) e({Q}(x)(y)-{Q}(x)(x))\, d\mu (y). \end{equation}
4.0.1

Proof

Fix \(x\in G\setminus G'\). Sorting the tiles \({\mathfrak p}\) on the left-hand-side of 4.0.1 by the value \({\mathrm{s}}({\mathfrak p})\in [-S,S]\), it suffices to prove for every \(-S\le s\le S\) that

\begin{equation} \label{outsump} \sum _{{\mathfrak p}\in {\mathfrak P}: {\mathrm{s}}({\mathfrak p})=s}T_{{\mathfrak p}} f(x)=0 \end{equation}
4.0.2

if \(s\not\in [\sigma _1(x), \sigma _2(x)]\) and

\begin{equation} \label{insump} \sum _{{\mathfrak p}\in {\mathfrak P}: {\mathrm{s}}({\mathfrak p})=s}T_{{\mathfrak p}} f(x)= \int K_{s}(x,y) f(y) e({Q}(x)(y) - {Q}(x)(x))\, d\mu (y). \end{equation}
4.0.3

if \(s\in [\sigma _1(x),\sigma _2(x)]\). If \(s\not\in [\sigma _1(x), \sigma _2(x)]\), then by definition of \(E({\mathfrak p})\) we have \(x\not\in E({\mathfrak p})\) for any \({\mathfrak p}\) with \({\mathrm{s}}({\mathfrak p})=s\) and thus \(T_{{\mathfrak p}} f(x)=0\). This proves 4.0.2.

Now assume \(s\in [\sigma _1(x),\sigma _2(x)]\). By 2.0.7, 2.0.9, 2.0.10, the fact that \(c(I_0) = o\) and \(G\subset B(o,\frac14 D^S)\), there is at least one \(I\in \mathcal{D}\) with \(s(I)=s\) and \(x\in I\). By 2.0.8, this \(I\) is unique. By 2.0.13, there is precisely one \({\mathfrak p}\in {\mathfrak P}(I)\) such that \({Q}(x)\in {\Omega }({\mathfrak p})\). Hence there is precisely one \({\mathfrak p}\in {\mathfrak P}\) with \({\mathrm{s}}({\mathfrak p})=s\) such that \(x\in E({\mathfrak p})\). For this \({\mathfrak p}\), the value \(T_{{\mathfrak p}}(x)\) by its definition in 2.0.21 equals the right-hand side of 4.0.3. This proves the lemma.

We use this to prove Proposition 2.0.1.

Proof of Proposition 2.0.1

We now estimate with Lemma 4.0.3 and Proposition 2.0.2

\begin{equation} \int _{G \setminus G'} \left|\sum _{s={\sigma _1}(x)}^{{\sigma _2}(x)} \int K_s(x,y) f(y) e({Q}(x)(y)) \, \mathrm{d}\mu (y)\right| \mathrm{d}\mu (x) \end{equation}
4.0.4

\begin{equation} =\int _{G \setminus G'} \left|\sum _{s={\sigma _1}(x)}^{{\sigma _2}(x)} \int K_s(x,y) f(y) e({Q}(x)(y) - {Q}(x)(x))\mathrm{d}\mu (y)\right| \mathrm{d}\mu (x) \end{equation}
4.0.5

\begin{equation} =\int _{G \setminus G'} \left|\sum _{{\mathfrak p}\in {\mathfrak P}}T_{{\mathfrak p}} f(x)\right| \mathrm{d}\mu (x) \le \frac{2^{440a^3}}{(q-1)^5} \mu (G)^{1 - \frac{1}{q}} \mu (F)^{\frac{1}{q}} \, . \end{equation}
4.0.6

This proves 2.0.6 for the chosen set \(G'\) and arbitrary \(f\) and thus completes the proof of Proposition 2.0.1.

4.1 Proof of Grid Existence Lemma

We begin with the construction of the centers of the dyadic cubes.

Lemma 4.1.1 counting balls
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Let \(-S\le k\le S\). Consider \(Y\subset X\) such that for any \(y\in Y\), we have

\begin{equation} \label{ybinb} y\in B(o,4D^S-D^k), \end{equation}
4.1.1

furthermore, for any \(y'\in Y\) with \(y\neq y'\), we have

\begin{equation} \label{eq-disj-yballs} B(y,D^k)\cap B(y',D^k)=\emptyset . \end{equation}
4.1.2

Then the cardinality of \(Y\) is bounded by

\begin{equation} \label{boundY} |Y|\le 2^{3a + 200Sa^3}\, . \end{equation}
4.1.3

Proof

Let \(k\) and \(Y\) be given. By applying the doubling property 1.0.5 inductively, we have for each integer \(j\ge 0\)

\begin{equation} \label{jballs} \mu (B(y,2^{j}D^k))\le 2^{aj} \mu (B(y,D^k))\, . \end{equation}
4.1.4

Since \(X\) is the union of the balls \(B(y,2^{j}D^k)\) and \(\mu \) is not zero, at least one of the balls \(B(y,2^{j}D^k)\) has positive measure, thus \(B(y,D^k)\) has positive measure.

Applying 4.1.4 for \(j' = \ln _2(8D^{2S}) = 3 + 2S \cdot 100a^2\) by 2.0.1, using \(-S\le k\le S\), \(y\in B(o,4D^S)\), and the triangle inequality, we have

\begin{equation} B(o, 4D^S) \subset B(y, 8D^S) \subset B(y,2^{j'}D^k) \, . \end{equation}
4.1.5

Using the disjointedness of the balls in 4.1.2, 4.1.1, and the triangle inequality for \(\rho \), we obtain

\begin{equation} |Y|\mu (B(o,4D^S))\le 2^{j'a}\sum _{y\in Y}\mu (B(y,D^k)) \end{equation}
4.1.6

\begin{equation} \le 2^{j'a}\mu (\bigcup _{y\in Y}B(y,D^k)) \le 2^{j'a}\mu (o,4D^S)\, . \end{equation}
4.1.7

As \(\mu (o,4D^S)\) is not zero, the lemma follows.

For each \(-S\le k\le S\), let \(Y_k\) be a set of maximal cardinality in \(X\) such that \(Y=Y_k\) satisfies the properties 4.1.1 and 4.1.2 and such that \(o \in Y_k\). By the upper bound of Lemma 4.1.1, such a set exists.

For each \(-S\le k\le S\), choose an enumeration of the points in the finite set \(Y_k\) and thus a total order \({\lt}\) on \(Y_{k}\).

Lemma 4.1.2 cover big ball
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For each \(-S\le k\le S\), the ball \(B(o, 4D^S-D^k)\) is contained in the union of the balls \(B(y,2D^k)\) with \(y\in Y_k\).

Proof

Let \(x\) be any point of \(B(o, 4D^S-D^k)\). By maximality of \(|Y_k|\), the ball \(B(x, D^k)\) intersects one of the balls \(B(y, D^k)\) with \(y\in Y_k\). By the triangle inequality, \(x\in B(y,2D^k)\).

Define the set

\begin{equation} \mathcal{C}:= \{ (y,k): -S\le k\le S, y\in Y_k\} \, \end{equation}
4.1.8

We totally order the set \(\mathcal{C}\) lexicographically by setting \((y,k){\lt}(y',k')\) if \(k{\lt} k'\) or both \(k=k'\) and \(y{\lt}y'\). In what follows, we define recursively in the sense of this order a function

\begin{equation} (I_1,I_2,I_3): \mathcal{C}\to \mathcal{P}(X)\times \mathcal{P}(X)\times \mathcal{P}(X)\, . \end{equation}
4.1.9

Assume the sets \({I}_j(y',k')\) have already been defined for \(j=1,2,3\) if \(k'{\lt}k\) and if \(k=k'\) and \(y'{\lt}y\).

If \(k=-S\), define for \(j\in \{ 1,2\} \) the set \({I}_j(y,k)\) to be \(B(y,jD^{-S})\). If \(-S{\lt}k\), define for \(j\in \{ 1,2\} \) and \(y\in Y_k\) the set \({I}_j(y,k)\) to be

\begin{equation} \label{defineij} \bigcup \{ I_3(y',k-1): y'\in Y_{k-1}\cap B(y,jD^k)\} . \end{equation}
4.1.10

Define for \(-S\leq k\leq S\) and \(y\in Y_k\)

\begin{equation} \label{definei3} I_3(y,k):={I_1}(y,k)\cup \left[{I_2}(y,k)\setminus \left[X_k\cup \bigcup \{ I_3(y',k):y'\in Y_{k}, y'{\lt}y\} )\right]\right] \end{equation}
4.1.11

with

\begin{equation} X_{k}:=\bigcup \{ I_1(y', k):y'\in Y_{k}\} . \end{equation}
4.1.12

Lemma 4.1.3 basic grid structure

For each \(-S\le k\le S\) and \(1\le j\le 3\) the following holds.

If \(j\neq 2\) and for some \(x\in X\) and \(y_1,y_2\in Y_k\) we have

\begin{equation} \label{disji} x\in I_j(y_1,k)\cap I_j(y_2,k), \end{equation}
4.1.13

then \(y_1=y_2\).

If \(j\neq 1\), then

\begin{equation} \label{unioni} B(o, 4D^S-2D^k)\subset \bigcup _{y\in Y_k} I_j(y,k)\, . \end{equation}
4.1.14

We have for each \(y\in Y_k\),

\begin{equation} \label{squeezedyadic} B(y,\frac12 D^k) \subset I_3(y,k)\subset B(y,4D^k). \end{equation}
4.1.15

Proof

We prove these statements simultaneously by induction on the ordered set of pairs \((y,k)\). Let \(-S\le k\le S\).

We first consider 4.1.13 for \(j=1\). If \(k=-S\), disjointedness of the sets \(I_1(y,-S)\) follows by definition of \(I_1\) and \(Y_k\). If \(k{\gt}-S\), assume \(x\) is in \(I_1(y_m,k)\) for \(m=1,2\). Then, for \(m=1,2\), there is \(z_m\in Y_{k-1}\cap B(y_m,D^k)\) with \(x\in I_3(z_m,k-1)\). Using 4.1.13 inductively for \(j=3\), we conclude \(z_1=z_2\). This implies that the balls \(B(y_1, D^k)\) and \(B(y_2, D^k)\) intersect. By construction of \(Y_k\), this implies \(y_1=y_2\). This proves 4.1.13 for \(j=1\).

We next consider 4.1.13 for \(j=3\). Assume \(x\) is in \(I_3(y_m,k)\) for \(m=1,2\) and \(y_m\in Y_k\). If \(x\) is in \(X_k\), then by definition 4.1.11, \(x\in I_1(y_m,k)\) for \(m=1,2\). As we have already shown 4.1.13 for \(j=1\), we conclude \(y_1=y_2\). This completes the proof in case \(x\in X_k\), and we may assume \(x\) is not in \(X_k\). By definition 4.1.11, \(x\) is not in \(I_3(z,k)\) for any \(z\) with \(z{\lt}y_1\) or \(z{\lt}y_2\). Hence, neither \(y_1{\lt}y_2\) nor \(y_2{\lt}y_1\), and by totality of the order of \(Y_k\), we have \(y_1=y_2\). This completes the proof of 4.1.13 for \(j=3\).

We show 4.1.14 for \(j=2\). In case \(k=-S\), this follows from Lemma 4.1.2. Assume \(k{\gt}-S\). Let \(x\) be a point of \(B(o, 4D^S-2D^k)\). By induction, there is \(y'\in Y_{k-1}\) such that \(x\in I_3(y',k-1)\). Using the inductive statement 4.1.15, we obtain \(x\in B(y',4D^{k-1})\). As \(D{\gt}4\), by applying the triangle inequality with the points, \(o\), \(x\), and \(y'\), we obtain that \(y'\in B(o, 4D^S-D^k)\). By Lemma 4.1.2, \(y'\) is in \(B(y,2D^k)\) for some \(y\in Y_k\). It follows that \(x\in I_2(y,k)\). This proves 4.1.14 for \(j=2\).

We show 4.1.14 for \(j=3\). Let \(x\in B(o, 4D^S-2D^k)\). In case \(x\in X_k\), then by definition of \(X_k\) we have \(x\in I_1(y,k)\) for some \(y\in Y_k\) and thus \(x\in I_3(y,k)\). We may thus assume \(x\not\in X_k\). As we have already seen 4.1.14 for \(j=2\), there is \(y\in Y_k\) such that \(x\in I_2(y,k)\). We may assume this \(y\) is minimal with respect to the order in \(Y_k\). Then \(x\in I_3(y,k)\). This proves 4.1.14 for \(j=3\).

Next, we show the first inclusion in 4.1.15. Let \(x\in B(y,\frac12 D^k)\). As \(I_1(y,k)\subset I_3(y,k)\), it suffices to show \(x\in I_1(y,k)\). If \(k=-S\), this follows immediately from the assumption on \(x\) and the definition of \(I_1\). Assume \(k{\gt}-S\). By the inductive statement 4.1.14 and \(D{\gt}4\), there is a \(y'\in Y_{k-1}\) such that \(x\in I_3(y',k-1)\). By the inductive statement 4.1.15, we conclude \(x\in B(y',4D^{k-1})\). By the triangle inequality with points \(x\), \(y\), \(y'\), and \(D\geq 8\), we have \(y'\in B(y,D^k)\). It follows by definition 4.1.10 that \(I_3(y',k-1)\subset I_1(y,k)\), and thus \(x\in I_3(y,k)\). This proves the first inclusion in 4.1.15.

We show the second inclusion in 4.1.15. Let \(x\in I_3(y,k)\). As \(I_1(y,k)\subset I_2(y,k)\) directly from the definition 4.1.10, it follows by definition 4.1.11 that \(x\in I_2(y,k)\). By definition 4.1.10, there is \(y'\in Y_{k-1}\cap B(y,2D^k)\) with \(x\in I_3(y',k-1)\). By induction, \(x\in B(y', 4D^{k-1})\). By the triangle inequality applied to the points \(x,y',y\) and \(D{\gt}4\), we conclude \(x\in B(y,4D^k)\). This shows the second inclusion in 4.1.15 and completes the proof of the lemma.

Lemma 4.1.4 cover by cubes
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Let \(-S\le l\le k\le S\) and \(y\in Y_k\). We have

\begin{equation} \label{3coverdyadic} I_3(y,k)\subset \bigcup _{y'\in Y_l} I_3(y',l)\, . \end{equation}
4.1.16

Proof

Let \(-S\le l\le k\le S\) and \(y\in Y_k\). If \(l=k\), the inclusion 4.1.16 is true from the definition of set union. We may then assume inductively that \(k{\gt}l\) and the statement of the lemma is true if \(k\) is replaced by \(k-1\). Let \(x\in I_3(y,k)\). By definition 4.1.11, \(x\in I_j(y,k)\) for some \(j\in \{ 1,2\} \). By 4.1.10, \(x\in I_3(w,k-1)\) for some \(w\in Y_{k-1}\). We conclude 4.1.16 by induction.

Lemma 4.1.5 dyadic property
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Let \(-S\le l\le k\le S\) and \(y\in Y_k\) and \(y'\in Y_l\) with \(I_3(y',l)\cap I_3(y,k)\neq \emptyset \). Then

\begin{equation} \label{3dyadicproperty} I_3(y',l)\subset I_3(y,k). \end{equation}
4.1.17

Proof

Let \(l,k,y,y'\) be as in the lemma. Pick \(x\in I_3(y',l)\cap I_3(y,k)\). Assume first \(l=k\). By 4.1.13 of Lemma 4.1.3, we conclude \(y'=y\), and thus 4.1.17. Now assume \(l{\lt}k\). By induction, we may assume that the statement of the lemma is proven for \(k-1\) in place of \(k\).

By Lemma 4.1.4, there is a \(y''\in Y_{k-1}\) such that \(x\in I_3(y'',k-1)\). By induction, we have \(I_3(y',l)\subset I_3(y'',k-1)\). It remains to prove

\begin{equation} \label{wyclaim} I_3(y'',k-1)\subset I_3(y,k). \end{equation}
4.1.18

We make a case distinction and assume first \(x\in X_k\). By Definition 4.1.11, we have \(x\in I_1(y,k)\). By Definition 4.1.10, there is a \(v\in Y_{k-1}\cap B(y,D^k)\) with \(x\in I_3(v,k-1)\). By 4.1.13 of Lemma 4.1.3, we have \(v=y''\). By Definition 4.1.10, we then have \(I_3(y'',k-1)\subset I_1(y,k)\). Then 4.1.18 follows by Definition 4.1.11 in the given case.

Assume now the case \(x\notin X_k\). By 4.1.11, we have \(x\in I_2(y,k)\). Moreover, for any \(u{\lt}y\) in \(Y_k\), we have \(x\not\in I_3(u,k)\). Let \(u{\lt}y\). By transitivity of the order in \(Y_k\), we conclude \(x\not\in I_2(u,k)\). By 4.1.10 and the disjointedness property of Lemma 4.1.3, we have \(I_3(y'',k-1)\cap I_2(u,k)= \emptyset \). Similarly, \(I_3(y'',k-1)\cap I_1(u,k)= \emptyset \). Hence \(I_3(y'',k-1)\cap I_3(u,k)=\emptyset \). As \(u{\lt}y\) was arbitrary, we conclude with 4.1.11 the claim in the given case. This completes the proof of 4.1.18, and thus also 4.1.17.

For \(-S\le k'\le k\le S\) and \(y'\in Y_{k'}\), \(y\in Y_k\) write \((y',k'|y,k)\) if \(I_3(y',k')\subset I_3(y,k)\) and

\begin{equation} \label{bdcond} \inf _{x\in X\setminus I_3(y,k)}\rho (y',x){\lt}6D^{k'}\, . \end{equation}
4.1.19

Lemma 4.1.6 transitive boundary
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Assume \(-S\le k''{\lt} k'{\lt} k\le S\) and \(y''\in Y_{k''}\), \(y'\in Y_{k'}\), \(y\in Y_k\). Assume there is \(x\in X\) such that

\begin{equation} x\in I_3(y'',k'')\cap I_3(y',k')\cap I_3(y,k)\, . \end{equation}
4.1.20

If \((y'',k''|y,k)\), the also \((y'',k''|y',k')\) and \((y',k'|y,k)\)

Proof

As \(x\in I_3(y'',k'')\cap I_3(y',k')\) and \(k''{\lt} k'\), we have by Lemma 4.1.5 that \(I_3(y'',k'')\subset I_3(y',k')\). Similarly, \(I_3(y',k')\subset I_3(y,k)\). Pick \(x'\in X\setminus I_3(y,k)\) such that

\begin{equation} \label{yppxp} \rho (y'',x'){\lt} 6D^{k''}\, , \end{equation}
4.1.21

which exists as \((y'',k''|y,k)\). As \(x'\in X\setminus I_3(y',k')\) as well, we conclude \((y'',k''| y',k')\). By the triangle inequality, we have

\begin{equation} \rho (y',x')\le \rho (y',x)+\rho (x,y'')+\rho (y'',x') \end{equation}
4.1.22

Using the choice of \(x\) and 4.1.15 as well as 4.1.21, we estimate this by

\begin{equation} {\lt} 4D^{k'}+4D^{k''}+6D^{k''}\le 6D^{k'}\, , \end{equation}
4.1.23

where we have used \(D{\gt}5\) and \(k''{\lt}k'\). We conclude \((y',k'|y,k)\).

Lemma 4.1.7 small boundary
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Let \(K = 2^{4a+1}\). For each \(-S+K\le k\le S\) and \(y\in Y_k\) we have

\begin{equation} \label{new-small-boundary} \sum _{z\in Y_{k-K}: (z,k-K|y,k)}\mu (I_3(z,k-K)) \le \frac12 \mu (I_3(y,k))\, . \end{equation}
4.1.24

Proof

Let \(K\) be as in the lemma. Let \(-S+K\le k\le S\) and \(y\in Y_k\).

Pick \(k'\) so that \(k-K\le k'\le k\). For each \(y''\in Y_{k-K}\) with \((y'',k-K| y,k)\), by Lemma 4.1.4 and Lemma 4.1.5, there is a unique \(y'\in Y_{k'}\) such that

\begin{equation} \label{4.31} I_3(y'',k-K)\subset I_3(y',k')\subset I_3(y,k)\, . \end{equation}
4.1.25

Using Lemma 4.1.6, \((y',k'|y,k)\).

We conclude using the disjointedness property of Lemma 4.1.3 that

\begin{equation} \label{scalecompare} \sum _{y'': (y'',k-K|y,k)}\mu (I_3(y'',k-K)) \le \sum _{y': (y',k'|y,k)} \mu (I_3(y',k')) \, . \end{equation}
4.1.26

Adding over \(k-K{\lt}k'\le k\), and using

\[ \mu (I_3(y',k'))\le 2^{4a} \mu (B(y', \frac14 D^{k'})) \]

from the doubling property 1.0.5 and 4.1.15 gives

\begin{equation} \label{sumcompare} K\sum _{y'': (y'',k-K|y,k)} \mu (I_3(y'',k-K)) \end{equation}
4.1.27

\begin{equation} \label{sumcompare1} \le 2^{4a} \sum _{k-K{\lt}k'\le k} \left[ \sum _{y': (y',k'|y,k)} \mu (B(y', \frac14 D^{k'}))\right] \end{equation}
4.1.28

Each ball \(B(y', \frac14 D^{k'})\) occurring in 4.1.28 is contained in \(I_3(y',k')\) by 4.1.15 and in turn contained in \(I_3(y,k)\) by 4.1.25. Assume for the moment all these balls are pairwise disjoint. Then by additivity of the measure,

\begin{equation} K\sum _{y'': (y'',k-K|y,k)} \mu (I_3(y'',k-K)) \le 2^{4a} \mu (I_3(y,k))\, \end{equation}
4.1.29

which by \(K=2^{4a+1}\) implies 4.1.24.

It thus remains to prove that the balls occurring in 4.1.28 are pairwise disjoint. Let \((u,l)\) and \((u',l')\) be two parameter pairs occurring in the sum of 4.1.28 and let \( B(u, \frac14 D^l)\) and \(B({u’}, \frac14 D^{l'})\) be the corresponding balls. If \(l=l'\), then the balls are equal or disjoint by 4.1.15 and 4.1.13 of Lemma 4.1.3. Assume then without loss of generality that \(l'{\lt}l\). Towards a contradiction, assume that

\begin{equation} \label{bulbul} B(u, \frac14 D^l)\cap B({u’}, \frac14 D^{l'})\neq \emptyset \end{equation}
4.1.30

As \((u',l'|y,k)\), there is a point \(x\) in \(X\setminus I_3(y,k)\) with \(\rho (x,u'){\lt}6D^{l'}\). Using \(D{\gt}25\), we conclude from the triangle inequality and 4.1.30 that \(x\in B(u,\frac12D^l)\). However, \(B(u,\frac12 D^l)\subset I_3(u,l)\), and \(I_3(u,l)\subset I_3(y,k)\), a contradiction to \(x\not\in I_3(y,k)\). This proves the lemma.

Lemma 4.1.8 smaller boundary
#

Let \(K = 2^{4a+1}\) and let \(n\ge 0\) be an integer. Then for each \(-S+nK\le k\le S\) we have

\begin{equation} \label{very-new-small} \sum _{y'\in Y_{k-nK}: (y',k-nK|y,k)}\mu (I_3(y',k-nK)) \le 2^{-n} \mu (I_3(y,k))\, . \end{equation}
4.1.31

Proof

We prove this by induction on \(n\). If \(n=0\), both sides of 4.1.31 are equal to \(\mu (I_3(y,k))\) by 4.1.13. If \(n=1\), this follows from Lemma 4.1.7.

Assume \(n{\gt}1\) and 4.1.31 has been proven for \(n-1\). We write 4.1.31

\begin{equation} \sum _{y''\in Y_{k-nK}: (y'',k-nK|y,k)}\mu (I_3(y'',k-nK)) \end{equation}
4.1.32

\begin{equation} = \sum _{y'\in Y_{k-K}:(y',k-K|y,k)} \left[ \sum _{y''\in Y_{k-nK}: (y'',k-nK|y',k-K)}\mu (I_3(y'',k-nK)) \right] \end{equation}
4.1.33

Applying the induction hypothesis, this is bounded by

\begin{equation} = \sum _{y'\in Y_{k-K}:(y',k-K|y,k)} 2^{1-n}\mu (I_3(y',k-K)) \end{equation}
4.1.34

Applying 4.1.24 gives 4.1.31, and proves the lemma.

Lemma 4.1.9 boundary measure
#

For each \(-S\le k\le S\) and \(y\in Y_k\) and \(0{\lt}t{\lt}1\) with \(tD^k\ge D^{-S}\) we have

\begin{equation} \label{old-small-boundary} \mu (\{ x \in I_3(y,k) \ : \ \rho (x, X \setminus I_3(y,k)) \leq t D^{k}\} ) \le 2 t^\kappa \mu (I_3(y,k))\, . \end{equation}
4.1.35

Proof

Let \(x\in I_3(y,k)\) with \(\rho (x, X \setminus I_3(y,k)) \leq t D^{k}\). Let \(K = 2^{4a+1}\) as in Lemma 4.1.8. Let \(n\) be the largest integer such that \(D^{nK} \le \frac{1}{t}\), so that \(tD^k \le D^{k-nK}\) and

\begin{equation} \label{eq-n-size} D^{nK} {\gt} \frac{1}{tD^K}\, . \end{equation}
4.1.36

Let \(k' = k - nK\), by the assumption \(tD^k \ge D^{-S}\), we have \(k' \ge -S\). By 4.1.16, there exists \(y' \in Y_{k'}\) with \(x \in I_3(y',k')\). By the squeezing property 4.1.15 and the assumption on \(x\), we have

\[ \rho (y', X \setminus I_3(y,k)) \le \rho (x,y') + \rho (x, X \setminus I_3(y,k)) \le 4 D^{k'} + t D^{k}\, . \]

By the assumption on \(n\) and the definition of \(k'\), this is

\[ \le 4D^{k'} + D^{k - nK} {\lt} 6D^{k'}\, . \]

Together with 4.1.17 thus \((y',k'|y,k)\). We have shown that

\[ \{ x \in I_3(y,k) \ : \ \rho (x, X \setminus I_3(y,k)) \leq t D^{k}\} \]
\[ \subset \bigcup _{y'\in Y_{k-nK}: (y',k-nK|y,k)}I_3(y',k-nK)\, . \]

Using monotonicity and additivity of the measure and Lemma 4.1.8, we obtain

\[ \mu (\{ x \in I_3(y,k) \ : \ \rho (x, X \setminus I_3(y,k)) \leq t D^{k}\} ) \le 2^{-n} \mu (I_3(y,k))\, . \]

By 4.1.36 and the definition 2.0.1 of \(D\), this is bounded by

\[ 2 t^{1/(100a^2 K)} \mu (I_3(y,k))\, , \]

which completes the proof by the definition 2.0.2 of \(\kappa \).

Let \(\tilde{\mathcal{D}}\) be the set of all \(I_3(y,k)\) with \(k\in [-S,S]\) and \(y\in Y_k\). Define

\begin{equation} s(I_3(y,k)):=k \end{equation}
4.1.37

\begin{equation} c(I_3(y,k)):=y\, . \end{equation}
4.1.38

We define \(\mathcal{D}\) to be the set of all \(I \in \tilde{\mathcal{D}}\) such that \(I \subset I_3(o, S)\).

Proof of Lemma 4.0.1

We first show that \((\tilde{\mathcal{D}},c,s)\) satisfies properties 2.0.7, 2.0.8, 2.0.10 and 2.0.11. Property 2.0.10 follows from 4.1.15, while 2.0.11 follows from Lemma 4.1.9.

Let \(x\in B(o, D^S)\). We show properties 2.0.7 and 2.0.8 for \((\tilde{\mathcal{D}},c,s)\) and \(x\).

We first show 2.0.7 for \((\tilde{\mathcal{D}},c,s)\) by contradiction. Then there is an \(I\) violating the conclusion of 2.0.7. Pick such \(I=I_3(y,l)\) such that \(l\) is minimal. By assumption, we have \(-S\le k{\lt}l\); in particular \(-S{\lt}l\). By definition, \(I_3(y, l)\) is contained in \(I_1(y, l)\cup I_2(y, l)\), which is contained in the union of \(I_3(y',l-1)\) with \(y'\in Y_{l-1}\). By minimality of \(l\), each such \(I_3(y',l-1)\) is contained in the union of all \(I_3(z,k)\) with \(z\in Y_k\). This proves 2.0.7.

We now show 2.0.8 for \((\tilde{\mathcal{D}},c,s)\). Assume to get a contradiction that there are non-disjoint \(I, J\in \tilde{\mathcal{D}}\) with \(s(I)\le s(J)\) and \(I \not\subset J\). We may assume the existence of such \(I\) and \(J\) with minimal \(s(J)-s(I)\). Let \(k=s(I)\). Assume first \(s(J)=k\). Let \(I=I_3(y_1,k)\) and \(J=I_3(y_2,k)\) with \(y_1,y_2\in Y_k\). If \(y_1=y_2\), then \(I=J\), a contradiction to \(I\not\subset J\). If \(y_1\neq y_2\), then \(I\cap J=\emptyset \) by 4.1.13, a contradiction to the non-disjointedness of \(I,J\). Assume now \(s(J){\gt}k\). Choose \(y\in I\cap J\). By property 2.0.7, there is \(K\in \tilde{\mathcal{D}}\) with \(s(K)=s(J)-1\) and \(y\in K\). By construction of \(J\), and pairwise disjointedness of all \(I_3(w,s(J)-1)\) that we have already seen, we have \(K\subset J\). By minimality of \(s(J)\), we have \(I\subset K\). This proves \(I\subset J\) and thus 2.0.8.

Now note that properties 2.0.8, 2.0.10 and 2.0.11 immediately carry over to \((\mathcal{D},c, s)\) by restriction. 2.0.9 is true for \((\mathcal{D}, c, s)\) by definition, and 2.0.7 follows from 2.0.7 and 2.0.8 for \((\tilde{\mathcal{D}}, c, s)\).

4.2 Proof of Tile Structure Lemma

Choose a grid structure \((\mathcal{D}, c, s)\) with Lemma 4.0.1 Let \(I \in \mathcal{D}\). Suppose that

\begin{equation} \label{eq-tile-Z} \mathcal{Z} \subset {Q}(X) \end{equation}
4.2.1

is such that for any \({\vartheta }, {\theta }\in \mathcal{Z}\) with \({\vartheta }\ne {\theta }\) we have

\begin{equation} \label{eq-tile-disjoint-Z} B_{I^\circ }({\vartheta }, 0.3) \cap B_{I^\circ }({\theta }, 0.3) \cap {Q}(X) = \emptyset \, . \end{equation}
4.2.2

Since \({Q}(X)\) is finite, there exists a set \(\mathcal{Z}\) satisfying both 4.2.1 and 4.2.2 of maximal cardinality among all such sets. We pick for each \(I \in \mathcal{D}\) such a set \(\mathcal{Z}(I)\).

Lemma 4.2.1 frequency ball cover
#

For each \(I \in \mathcal{D}\), we have

\begin{equation} \label{eq-tile-cover} {Q}(X) \subset \bigcup _{z \in \mathcal{Z}(I)} B_{I^\circ }(z, 0.7)\, . \end{equation}
4.2.3

Proof

Let \({\theta }\in \bigcup _{{\vartheta }\in {Q}(X)} B_{I^\circ }({\vartheta }, 1)\). By maximality of \(\mathcal{Z}(I)\), there must be a point \(z \in \mathcal{Z}(I)\) such that \(B_{I^\circ }(z, 0.3) \cap B_{I^\circ }({\theta }, 0.3) \ne \emptyset \). Else, \(\mathcal{Z}(I) \cup \{ {\theta }\} \) would be a set of larger cardinality than \(\mathcal{Z}(I)\) satisfying 4.2.1 and 4.2.2. Fix such \(z\), and fix a point \(z_1 \in B_{I^\circ }(z, 0.3) \cap B_{I^\circ }({\theta }, 0.3)\). By the triangle inequality, we deduce that

\[ d_{I^\circ }(z,{\theta }) \le d_{I^\circ }(z,z_1) + d_{I^\circ }({\theta }, z_1) {\lt} 0.3 + 0.3 = 0.6\, , \]

and hence \({\theta }\in B_{I^\circ }(z, 0.7)\).

We define

\[ {\mathfrak P}= \{ (I, z) \ : \ I \in \mathcal{D}, z \in \mathcal{Z}(I)\} \, , \]
\[ {\mathcal{I}}((I, z)) = I\qquad \text{and} \qquad {\mathcal{Q}}((I, z)) = z. \]

We further set

\[ {\mathrm{s}}({\mathfrak p}) = s({\mathcal{I}}({\mathfrak p})),\qquad \qquad {\mathrm{c}}({\mathfrak p}) = c({\mathcal{I}}({\mathfrak p})). \]

Then 2.0.18, 2.0.19 hold by definition.

It remains to construct the map \(\Omega \), and verify properties 2.0.13, 2.0.14 and 2.0.15. We first construct an auxiliary map \(\Omega _1\). For each \(I \in \mathcal{D}\), we pick an enumeration of the finite set \(\mathcal{Z}(I)\)

\[ \mathcal{Z}(I) = \{ z_1, \dotsc , z_M\} \, . \]

We define \(\Omega _1:{\mathfrak P}\mapsto \mathcal{P}({\Theta }) \) as below. Set

\[ \Omega _1((I, z_1)) = B_{I^\circ }(z_1, 0.7) \setminus \bigcup _{z \in \mathcal{Z}(I)\setminus \{ z_1\} } B_{I^\circ }(z, 0.3) \]

and then define iteratively

\begin{equation} \label{eq-def-omega1} \Omega _1((I, z_k)) = B_{I^\circ }(z_k, 0.7) \setminus \bigcup _{z \in \mathcal{Z}(I) \setminus \{ z_k\} } B_{I^\circ }(z, 0.3) \setminus \bigcup _{i=1}^{k-1} \Omega _1((I, z_i))\, . \end{equation}
4.2.4

Lemma 4.2.2 disjoint frequency cubes
#

For each \(I \in \mathcal{D}\), and \({\mathfrak p}_1, {\mathfrak p}_2\in {\mathfrak P}(I)\), if

\[ \Omega _1({\mathfrak p}_1)\cap \Omega _1({\mathfrak p}_2)\neq \emptyset , \]

then \({\mathfrak p}_1={\mathfrak p}_2\).

Proof

By the definition of the map \({\mathcal{I}}\), we have

\[ {\mathfrak P}(I) = \{ (I, z) \, : \, z \in \mathcal{Z}(I)\} \, . \]

By 4.2.4, the set \(\Omega _1((I, z_k))\) is disjoint from each \(\Omega _1((I, z_i))\) with \(i {\lt} k\). Thus the sets \(\Omega _1({\mathfrak p})\), \({\mathfrak p}\in {\mathfrak P}(I)\) are pairwise disjoint.

For each \(I \in \mathcal{D}\), it holds that

\begin{equation} \label{eq-omega1-cover} \bigcup _{z \in \mathcal{Z}(I)} B_{I^\circ }(z, 0.7)\subset \bigcup _{{\mathfrak p}\in {\mathfrak P}(I)} \Omega _1({\mathfrak p})\, . \end{equation}
4.2.5

For every \({\mathfrak p}\in {\mathfrak P}\), it holds that

\begin{equation} \label{eq-omega1-incl} B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}), 0.3) \subset \Omega _1({\mathfrak p}) \subset B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}), 0.7)\, . \end{equation}
4.2.6

Proof

For 4.2.6 let \({\mathfrak p}= (I, z)\). The second inclusion in 4.2.6 then follows from 4.2.4 and the equality \(B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}), 0.7) = B_{I^\circ }(z, 0.7)\), which is true by definition. For the first inclusion in 4.2.6 let \({\vartheta }\in B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}),0.3)\). Let \(k\) be such that \(z = z_k\) in the enumeration we chose above. It follows immediately from 4.2.4 and 4.2.2 that \({\vartheta }\notin \Omega _1((I, z_i))\) for all \(i {\lt} k\). Thus, again from 4.2.4, we have \({\vartheta }\in \Omega _1((I,z_k))\).

To show 4.2.5 let \({\vartheta }\in \bigcup _{z \in \mathcal{Z}(I)} B_{I^\circ }(z,0.7)\). If there exists \(z \in \mathcal{Z}(I)\) with \({\vartheta }\in B_{I^\circ }(z,0.3)\), then

\[ z \in \Omega _1((I, z)) \subset \bigcup _{{\mathfrak p}\in {\mathfrak P}(I)} \Omega _1({\mathfrak p}) \]

by the first inclusion in 4.2.6.

Now suppose that there exists no \(z \in \mathcal{Z}(I)\) with \({\vartheta }\in B_{I^\circ }(z, 0.3)\). Let \(k\) be minimal such that \({\vartheta }\in B_{I^\circ }(z_k, 0.7)\). Since \(\Omega _1((I, z_i)) \subset B_{I^\circ }(z_i, 0.7)\) for each \(i\) by 4.2.4, we have that \({\vartheta }\notin \Omega _1((I, z_i))\) for all \(i {\lt} k\). Hence \({\vartheta }\in \Omega _1((I, z_k))\), again by 4.2.4.

Now we are ready to define the function \(\Omega \). We define for all \({\mathfrak p}\in {\mathfrak P}(I_0)\)

\begin{equation} \label{eq-max-omega} {\Omega }({\mathfrak p}) = \Omega _1({\mathfrak p})\, . \end{equation}
4.2.7

For all other cubes \(I \in \mathcal{D}\), \(I \ne I_0\), there exists, by 2.0.8 and 2.0.9, \(J \in \mathcal{D}\) with \(I \subset J\) and \(I \ne J\). On such \(I\) we define \(\Omega \) by recursion. We can pick an inclusion minimal \(J \in \mathcal{D}\) among the finitely many cubes such that \(I \subset J\) and \(I \ne J\). This \(J\) is unique: Suppose that \(J'\) is another inclusion minimal cube with \(I \subset J'\) and \(I \ne J'\). Without loss of generality, we have that \(s(J) \le s(J')\). By 2.0.8, it follows that \(J \subset J'\). Since \(J'\) is minimal with respect to inclusion, it follows that \(J = J'\). Then we define

\begin{equation} \label{eq-it-omega} {\Omega }({\mathfrak p}) = \bigcup _{z \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p})} \Omega ((J, z)) \cup B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}),0.2)\, . \end{equation}
4.2.8

We now verify that \(({\mathfrak P},{\mathcal{I}},{\Omega },{\mathcal{Q}},{\mathrm{c}},{\mathrm{s}})\) forms a tile structure.

Proof of Lemma 4.0.2

First, we prove 2.0.15. If \(I =I_0\), then 2.0.15 holds for all \({\mathfrak p}\in {\mathfrak P}(I)\) by 4.2.7 and 4.2.6. Now suppose that \(I\) is not maximal in \(\mathcal{D}\) with respect to set inclusion. Then we may assume by induction that for all \(J \in \mathcal{D}\) with \(I \subset J\) and all \({\mathfrak p}' \in {\mathfrak P}(J)\), 2.0.15 holds. Let \(J\) be the unique minimal cube in \(\mathcal{D}\) with \(I \subsetneq J\).

Suppose that \({\vartheta }\in \Omega ({\mathfrak p})\). If \({\vartheta }\in B_{{\mathfrak p}}(\mathcal{Q}({\mathfrak p}), 0.2)\), then since

\begin{equation*} B_{{\mathfrak p}}(\mathcal{Q}({\mathfrak p}), 0.2)\subset B_{{\mathfrak p}}(\mathcal{Q}({\mathfrak p}), 1)\, , \end{equation*}

we conclude that \({\vartheta }\in B_{{\mathfrak p}}(\mathcal{Q}({\mathfrak p}), 0.7)\). If not, by 4.2.8, there exists \(z \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p})\) with \({\vartheta }\in \Omega (J,z)\). Using the triangle inequality and 4.2.6, we obtain

\[ d_{I^\circ }({\mathcal{Q}}({\mathfrak p}),{\vartheta }) \le d_{I^\circ }({\mathcal{Q}}({\mathfrak p}), z) + d_{I^\circ }(z, {\vartheta }) \le 0.7 + d_{I^\circ }(z, {\vartheta })\, . \]

By Lemma 2.1.2 and the induction hypothesis, this is estimated by

\[ \le 0.7 + 2^{-95a} d_{J^\circ }(z,{\vartheta }) \le 0.7 + 2^{-95a}\cdot 1 {\lt} 1\, . \]

This shows the second inclusion in 2.0.15. The first inclusion is immediate from 4.2.8.

Next, we show 2.0.13. Let \(I \in \mathcal{D}\).

If \(I = I_0\), then disjointedness of the sets \({\Omega }({\mathfrak p})\) for \({\mathfrak p}\in {\mathfrak P}(I)\) follows from the definition 4.2.7 and Lemma 4.2.2. To obtain the inclusion in 2.0.13 one combines the inclusions 4.2.3 and 4.2.5 of Lemma 4.2.3 with 4.2.7.

Now we turn to the case where there exists \(J \in \mathcal{D}\) with \(I \subset J\) and \(I\ne J\). In this case we use induction: It suffices to show 2.0.13 under the assumption that it holds for all cubes \(J \in \mathcal{D}\) with \(I \subset J\). As shown before definition 4.2.8, we may choose the unique inclusion minimal such \(J\). To show disjointedness of the sets \({\Omega }({\mathfrak p}), {\mathfrak p}\in {\mathfrak P}(I)\) we pick two tiles \({\mathfrak p}, {\mathfrak p}' \in {\mathfrak P}(I)\) and \({\vartheta }\in {\Omega }({\mathfrak p}) \cap {\Omega }({\mathfrak p}')\). Then we are by 4.2.8 in one of the following four cases.

1. There exist \(z \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p})\) such that \({\vartheta }\in \Omega (J, z)\), and there exists \(z' \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p}')\) such that \({\vartheta }\in \Omega (J, z')\). By the induction hypothesis, that 2.0.13 holds for \(J\), we must have \(z = z'\). By Lemma 4.2.2, we must then have \({\mathfrak p}= {\mathfrak p}'\).

2. There exists \(z \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p})\) such that \({\vartheta }\in \Omega (J,z)\), and \({\vartheta }\in B_{{\mathfrak p}'}({\mathcal{Q}}({\mathfrak p}'), 0.2)\). Using the triangle inequality, Lemma 2.1.2 and 2.0.15, we obtain

\[ d_{{\mathfrak p}'}({\mathcal{Q}}({\mathfrak p}'),z) \le d_{{\mathfrak p}'}({\mathcal{Q}}({\mathfrak p}'), {\vartheta }) + d_{{\mathfrak p}'}(z, {\vartheta }) \le 0.2 + 2^{-95a} \cdot 1 {\lt} 0.3\, . \]

Thus \(z \in \Omega _1({\mathfrak p}')\) by 4.2.6. By Lemma 4.2.2, it follows that \({\mathfrak p}= {\mathfrak p}'\).

3. There exists \(z' \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p}')\) such that \({\vartheta }\in \Omega (J,z')\), and \({\vartheta }\in B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}), 0.2)\). This case is the same as case 2., after swapping \({\mathfrak p}\) and \({\mathfrak p}'\).

4. We have \({\vartheta }\in B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}), 0.2) \cap B_{{\mathfrak p}'}({\mathcal{Q}}({\mathfrak p}'), 0.2)\). In this case it follows that \({\mathfrak p}= {\mathfrak p}'\) since the sets \(B_{{\mathfrak p}}({\mathcal{Q}}({\mathfrak p}), 0.2)\) are pairwise disjoint by the inclusion 4.2.6 and Lemma 4.2.2.

To show the inclusion in 2.0.13, let \({\vartheta }\in {Q}(X)\). By the induction hypothesis, there exists \({\mathfrak p}\in {\mathfrak P}(J)\) such that \({\vartheta }\in \Omega ({\mathfrak p})\). By definition of the set \({\mathfrak P}\), we have \({\mathfrak p}= (J, z)\) for some \(z \in \mathcal{Z}(J)\). Thus, by 4.2.3, there exists \(z' \in \mathcal{Z}(I)\) with \(z \in B_{I^\circ }(z', 0.7)\). Then by Lemma 4.2.3 there exists \({\mathfrak p}' \in {\mathfrak P}(I)\) with \(z \in \mathcal{Z}(J) \cap \Omega _1({\mathfrak p}')\). Consequently, by 4.2.8, \({\vartheta }\in {\Omega }({\mathfrak p}')\). This completes the proof of 2.0.13.

Finally, we show 2.0.14. Let \({\mathfrak p}, {\mathfrak q}\in {\mathfrak P}\) with \({\mathcal{I}}({\mathfrak p}) \subset {\mathcal{I}}({\mathfrak q})\) and \({\Omega }({\mathfrak p}) \cap {\Omega }({\mathfrak q}) \ne \emptyset \). If we have \({\mathrm{s}}({\mathfrak p}) \ge {\mathrm{s}}({\mathfrak q})\), then it follows from 2.0.8 that \(I = J\), thus \({\mathfrak p}, {\mathfrak q}\in {\mathfrak P}(I)\). By 2.0.13 we have then either \({\Omega }({\mathfrak p}) \cap {\Omega }({\mathfrak q}) = \emptyset \) or \({\Omega }({\mathfrak p}) = {\Omega }({\mathfrak q})\). By the assumption in 2.0.14 we have \({\Omega }({\mathfrak p}) \cap {\Omega }({\mathfrak q}) \ne \emptyset \), so we must have \({\Omega }({\mathfrak p}) = {\Omega }({\mathfrak q})\) and in particular \({\Omega }({\mathfrak q}) \subset {\Omega }({\mathfrak p})\).

So it remains to show 2.0.14 under the additional assumption that \({\mathrm{s}}({\mathfrak q}) {\gt} {\mathrm{s}}({\mathfrak p})\). In this case, we argue by induction on \({\mathrm{s}}({\mathfrak q})-{\mathrm{s}}({\mathfrak p})\). By 2.0.7, there exists a cube \(J \in \mathcal{D}\) with \(s(J) = {\mathrm{s}}({\mathfrak q}) - 1\) and \(J \cap {\mathcal{I}}({\mathfrak p}) \ne \emptyset \). We pick one such \(J\). By 2.0.8, we have \({\mathcal{I}}({\mathfrak p}) \subset J \subset {\mathcal{I}}({\mathfrak q})\).

Thus, by 4.2.3, there exists \(z' \in \mathcal{Z}(J)\) with \({\mathcal{Q}}({\mathfrak q}) \in B_{J^\circ }(z', 0.7)\). Then by Lemma 4.2.3 there exists \({\mathfrak q}' \in {\mathfrak P}(J)\) with \({\mathcal{Q}}({\mathfrak q}) \in \Omega _1({\mathfrak q}')\). By 4.2.8, it follows that \(\Omega ({\mathfrak q}) \subset \Omega ({\mathfrak q}')\). Note that then \({\mathcal{I}}({\mathfrak p}) \subset {\mathcal{I}}({\mathfrak q}')\) and \({\Omega }({\mathfrak p}) \cap {\Omega }({\mathfrak q}') \ne \emptyset \) and \({\mathrm{s}}({\mathfrak q}') - {\mathrm{s}}({\mathfrak p}) = {\mathrm{s}}({\mathfrak q}) - {\mathrm{s}}({\mathfrak p}) - 1\). Thus, we have by the induction hypothesis that \(\Omega ({\mathfrak q}') \subset \Omega ({\mathfrak p})\). This completes the proof.