theorem
  G is independent implies All(Ex('not' a,A,G),B,G) '<' Ex('not' All(a,B
  ,G),A,G)
proof
A1: 'not' Ex(All(a,A,G),B,G) = All(Ex('not' a,A,G),B,G) by Th20;
  assume G is independent;
  hence thesis by A1,Th38;
end;
