theorem Th36:
  [[x, u], [y, v]] in ==>.-relation(TS) implies ex w st x, w -->.
  y, TS & u = w^v
proof
  assume [[x, u], [y, v]] in ==>.-relation(TS);
  then x, u ==>. y, v, TS by Def4;
  hence thesis;
end;
