This attribute should be set to a non-zero value if applying a
MathMap's forward transformation, followed immediately by the matching
inverse 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 AST_SIMPLIFY).
By default, the SimpFI attribute is zero, so that AST will not perform
this simplification unless you have set SimpFI to indicate that it is
safe to do so.