IsRealOnBothSides​(AngouriMath.​Entity,​AngouriMath.​Entity.​Variable,​AngouriMath.​Entity)

Whether expr is real on both sides of a real dest,
close enough to it, but for its constants, decided structurally: every power to an exponent that is not whole,
and every logarithm, has a base and an argument positive on both sides, by
SignNear(AngouriMath.Entity,AngouriMath.Entity.Variable,AngouriMath.Entity,AngouriMath.Core.ApproachFrom). Where it is, its one-sided limits are limits of values it takes on
either side, and their agreeing is the two-sided limit under any codomain. x^x is not, its base being negative on the left, and stays without one; (x^2)^x is,
and was NaN at 0 where each side is 1. Anything else unlisted is not real, which costs
coverage and never correctness.