theorem
  'not' Ex(Ex(a,A,G),B,G) '<' 'not' All(All(a,B,G),A,G)
proof
  All('not' Ex(a,A,G),B,G) '<' 'not' All(All(a,B,G),A,G) by Th28;
  hence thesis by BVFUNC_2:19;
end;
