isInverseMap  checks whether a rational map is the inverse of another
Synopsis

 Usage:
 isInverseMap(phi,psi)

Inputs:

phi, a ring map, representing a rational map $\Phi:X \dashrightarrow Y$

psi, a ring map, representing a rational map $\Psi:Y \dashrightarrow X$

Outputs:

a Boolean value, according to the condition that the composition $\Psi\,\Phi:X \dashrightarrow X$ coincides with the identity of $X$ (as a rational map)
Ways to use isInverseMap :