NormalTrigonometricForm

Four rules, and the first set here where every rule reverses: each writes one
of the four derived trigonometric functions in terms of sine and cosine, and both
sides are patterns, so reading a rule backwards recognises the quotient and puts the
name back. That direction is not run by anything today — it is the e-graph's
inverse-pair table that would — but it is now a property of the rules rather than a
second set someone has to write.