theorem Th40:
  crossover(p1,p2,n1,n2,n3,n4,n5) is Individual of S
proof
  reconsider q1=crossover(p1,p2,n1,n2,n3,n4), q2=crossover(p2,p1,n1,n2,n3,n4)
  as Individual of S;
  crossover(q1,q2,n5) is Individual of S;
  hence thesis;
end;
