This attribute should be set to a non-zero value if applying a
MathMap's inverse transformation, followed immediately by the matching
forward transformation will always restore the original set of
coordinates. It indicates that AST may replace such a sequence of
operations by an identity Mapping (a UnitMap) if it is encountered
while simplifying a compound Mapping (e.g. using astSimplify).
By default, the SimpIF attribute is zero, so that AST will not perform
this simplification unless you have set SimpIF to indicate that it is
safe to do so.