File non-covariance-of-generics.fmsl, line 17, char 3:
	Incompatible types in set expression.
    File non-covariance-of-generics.fmsl, line 19, char 3:
	Incompatible types in set expression.
    File non-covariance-of-generics.fmsl, line 20, char 3:
	Incompatible types in set expression.