RecursionError in sympy.solvers.inequalities.reduce_inequalities with custom function about sympy

[haru-44]

I think the correct behavior for sympy.solvers.inequalities.reduce_inequalities is to raise NotImplementedError because it assumes polynomial input.
However, sympy.calculus.util.periodicity does not behave as expected and results in a RecursionError. This is directly due to the reason that sympy.solvers.decompogen.decompogen does not expect a multivariable function.

sympy/sympy/solvers/decompogen.py

Lines 43 to 52 in 2eb826c

	# ===== Simple Functions ===== #
	if isinstance(f, (Function, Pow)):
	if f.is_Pow and f.base == S.Exp1:
	arg = f.exp
	else:
	arg = f.args[0]
	if arg == symbol:
	return [f]
	return [f.subs(arg, symbol)] + decompogen(arg, symbol)

Following this code only replaces the first argument, so decompogen(PythonMod(2*s0 + 3, s0 - 3), s0) returns [PythonMod(_x, _x - 3), 2*_x + 3]. Substituting 2*_x + 3 for PythonMod(_x, _x - 3) yields PythonMod(2*_x + 3, _x), which differs from the original expression.