fix potential unsoundness in Ty.ty_match
fix potential unsoundness in Ty.ty_match

ssaavedra/why3,douglas-larocca/why3,douglas-larocca/why3,ssaavedra/why3,jpdeplaix/why3,ssaavedra/why3,jpdeplaix/why3,jpdeplaix/why3,douglas-larocca/why3