Goal: feature parity with sympy

Edit this issue to make a plan that researches sympy bugs, features, tests, benchmarks, and follow its activity. Keep this issue open to track which sympy commit we have feature parity with. ToSympy should also work for all nodes that do have a sympy equivalent; ideally we have even more than them.

Start by researching SymPy bugs, features, tests, benchmarks, and recent activity, then compare those findings with AngouriMath's ToSympy coverage. Define a plan that identifies the SymPy commit used as the parity target and tracks support for every node with a SymPy equivalent.

Written by the indexing model from the issue text.