theorem Th6:
  for s being SortSymbol of S, x being set st x in (the Sorts of A)
  .s holds root-tree [x,s] is c-Term of A, V
proof
  let s be SortSymbol of S, x be set;
A1: ((the Sorts of A) (\/) V).s = (the Sorts of A).s \/ V.s by PBOOLE:def 4;
  assume x in (the Sorts of A).s;
  then x in ((the Sorts of A) (\/) V).s by A1,XBOOLE_0:def 3;
  then reconsider
  xs = [x,s] as Terminal of DTConMSA ((the Sorts of A) (\/) V) by MSAFREE:7;
  root-tree xs in TS DTConMSA ((the Sorts of A) (\/) V);
  hence thesis;
end;
