theorem Th33:
  for q,x,t,K,f st [All(x,q),t,K,f] in SepQuadruples p holds [q,t++,K \/ {x},
  f+*(x .--> x.t)] in SepQuadruples p
proof
  SepQuadruples(p) is_Sep-closed_on p by Def13;
  hence thesis;
end;
