theorem Th38:
  a [= b implies for a9,b9 being Element of L.: st a = a9 & b = b9
  holds b9 [= a9
proof
  assume a [= b;
  then
A1: a "\/" b = b;
  let a9,b9 be Element of L.:;
  assume a = a9 & b = b9;
  then b9 "/\" a9 = b9 by A1,Th37;
  hence thesis by LATTICES:4;
end;
