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

The powers k, of -1, 1, -2 and 2, for which
expr/candidate^k is one nonzero number at three
points, every other symbol pinned, agreeing to nine digits relative to its size. Each side
is evaluated once a point. A point where either cannot be evaluated admits no power: the
screen is all that keeps WithTheCandidatesPowerLeftInX(AngouriMath.Entity,AngouriMath.Entity,AngouriMath.Entity.Variable,AngouriMath.Entity.Variable) from simplifying. And
no ratio near zero, where two tiny values agree to any absolute tolerance:
x erfc(a + b x)^2 is 1e-9 at one pinned point and 1e-28 at the next.