theorem Th129:
  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
proof
  let S be non void Signature;
  let X be non empty ManySortedSet of the carrier of S;
A1: dom the Sorts of Free(S,X) = the carrier of S by PARTFUN1:def 2;
  let f be UnOp of Union the Sorts of Free(S,X);
A2: dom f = Union the Sorts of Free(S,X) by FUNCT_2:52;
  hereby
    assume
A3: f is term-transformation of S,X;
    let s be SortSymbol of S;
A4: f.:((the Sorts of Free(S,X)).s) c= (the Sorts of Free(S,X)).s by A3,Def56;
    (the Sorts of Free(S,X)).s in rng the Sorts of Free(S,X)
    by A1,FUNCT_1:def 3;
    then
A5: (the Sorts of Free(S,X)).s c= Union the Sorts of Free(S,X) by ZFMISC_1:74;
    let a be set;
    assume a in (the Sorts of Free(S,X)).s;
    then f.a in f.:((the Sorts of Free(S,X)).s) by A2,A5,FUNCT_1:def 6;
    hence f.a in (the Sorts of Free(S,X)).s by A4;
  end;
  assume
A6: 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;
  let s be SortSymbol of S;
  let x be object;
  assume x in f.:((the Sorts of Free(S,X)).s);
  then
  ex a being object
    st a in dom f & a in (the Sorts of Free(S,X)).s & x = f.a
  by FUNCT_1:def 6;
  hence thesis by A6;
end;
