reserve x,y,z,c for object,
  f for Function of 2-tuples_on BOOLEAN, BOOLEAN;

theorem
  for s being State of 1GateCircuit(x,y,f) holds (Following s).[<*x,y*>,
  f] = f.<*s.x, s.y*> & (Following s).x = s.x & (Following s).y = s.y by Th48;
