feat(Algebra/Notation/Indicator): pointwise evaluation of a function-valued indicator

[FrankieNC]

Adds Set.mulIndicator_apply_apply and its to_additive companion Set.indicator_apply_apply: for a family of functions f : α → β → M, s.mulIndicator f a b = s.mulIndicator (fun i ↦ f i b) a, so evaluating a function-valued indicator at b commutes with the indicator. It is the pointwise form of Set.mulIndicator_comp_of_one (with g the evaluation map at b).

[github-actions]

PR summary b6df78c734

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

+ mulIndicator_apply_apply

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit b6df78c).

• +2 new declarations
• −0 removed declarations

+Set.indicator_apply_apply
+Set.mulIndicator_apply_apply

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit b6df78c734
Reference commit f07d120284

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).