theorem Th33:
  x in ==>.-relation(TS) implies ex s, t, v, w st x = [[s, v], [t, w]]
proof
  assume
A1: x in ==>.-relation(TS);
  then consider y, z being object such that
A2: x = [y, z] by RELAT_1:def 1;
  ex s, v, t, w st y = [s, v] & z = [t, w] by A1,A2,Th31;
  hence thesis by A2;
end;
