reserve x,A,B,X,X9,Y,Y9,Z,V for set;

theorem
  A c= X & B c= Y & X misses Y implies A misses B
proof
  assume that
A1: A c= X and
A2: B c= Y and
A3: X misses Y;
  A misses Y by A1,A3,Th63;
  hence thesis by A2,Th63;
end;
