theorem Th32:
  a in F & b in F implies a "\/" b in F
proof
  assume a in F & b in F;
  then a` in F & b` in F by Def9;
  then a` "/\" b` in F by Def9;
  then ( a"\/"b )` in F by LATTICES:24;
  then ( a"\/"b )`` in F by Def9;
  hence thesis;
end;
