To express solution sets from solvers an expression-is-element-of-set relation is needed. For ease of implementation this can be made a formal function element_of.

It depends on sets being made coercible into SR. The present ticket plays safe and only does this for finite sets and a few standard infinite sets: NN, ZZ, QQ, AA; and RealSets.

element_of converts to SymPy's Contains. This is useful in combination with #31931, which adds SymPy conversions to some of the above sets.

Depends on #31877

CC: @videlec

Component: symbolics

Author: Ralf Stephan, Matthias Koeppe

Branch/Commit: a8c94ca

Reviewer: Travis Scrimshaw, Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/24171