subtract package:ghc-typelits-natnormalise

Subtract an inequality, in order to either:

• See if the smallest solution is a natural number
• Cancel sums, i.e. monotonicity of addition

subtractIneq (2*y <=? 3*x ~ True)  = (-2*y + 3*x)
subtractIneq (2*y <=? 3*x ~ False) = (-3*x + (-1) + 2*y)