for S being non void Signature
for X being non empty ManySortedSet of the carrier of S
for f being UnOp of (Union the Sorts of (Free (S,X))) holds
( f is term-transformation of S,X iff for s being SortSymbol of S
for a being set st a in the Sorts of (Free (S,X)) . s holds
f . a in the Sorts of (Free (S,X)) . s )