theorem Th49:
  'not' Ex(Ex(a,A,G),B,G) '<' Ex(All('not' a,B,G),A,G)
proof
  'not' Ex(Ex(a,A,G),B,G) '<' Ex('not' Ex(a,B,G),A,G) by Th43;
  hence thesis by BVFUNC_2:19;
end;
