Pome

Proposition 8.12.19989CBEEE646

Proposition 8.12.1.9989CBEEE646 Let $u,v$ be bounded admissible, put $w=\max \{ u,v\} $, and fix $1\leq p\leq m$. For any bounded admissible $t_2,\ldots ,t_ p$,

\[ \mathbf1_{\{ u>v\} }Q_ p(w,t_2,\ldots ,t_ p) =\mathbf1_{\{ u>v\} }Q_ p(u,t_2,\ldots ,t_ p). \]

The equality is coefficientwise as currents with measure coefficients. The corresponding equality on $\{ v>u\} $ follows by exchanging $u,v$.

Proof. Choose smooth uniformly bounded decreasing approximations of all the potentials by 8.6.6. Construct $w_ j$ by 8.2.9. Work on one compact coordinate test set. Fix $\delta >0$ and a smooth $\chi _\delta :\mathbb R\to [0,1]$ that vanishes for $s\leq \delta /2$ and equals one for $s\geq \delta $. For $j$ large enough that $\epsilon _ j<\delta /2$, ordinary smooth locality gives

\[ \chi _\delta (u_ j-v_ j)Q_ p(w_ j,t_2^ j,\ldots ,t_ p^ j) =\chi _\delta (u_ j-v_ j)Q_ p(u_ j,t_2^ j,\ldots ,t_ p^ j). \]

Indeed, wherever the weight is nonzero, $w_ j=u_ j$ on an open neighborhood. The equality elsewhere follows from its zero weight.

Both sequences of positive currents converge by 8.11.12; every coefficient variation is uniformly dominated by $C c_ m^*$ by 8.11.13. The potentials and their limits are quasicontinuous by 8.11.10. Apply 8.11.11 with $s=m$ and $F(x,y)=\chi _\delta (x-y)$ to the real and imaginary parts of each coefficient. Passing to the limit gives the same identity with $u,v,w,t_2,\ldots ,t_ p$. Choose the cutoffs so that $\chi _\delta (s)\to \mathbf1_{\{ s>0\} }$ pointwise as $\delta \downarrow 0$. Dominated convergence against the fixed finite coefficient variations on the test set gives the asserted restriction. A partition of unity proves it globally. $\square$

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