reserve D for non empty set;
reserve f1,f2 for FinSequence of D;
reserve i,n,n1,n2,n3,n4,n5,n6 for Element of NAT;
reserve S for Gene-Set;
reserve p1,p2 for Individual of S;

theorem Th6:
  crossover(p1,p2,n1,n2) is Individual of S
proof
  reconsider q1=crossover(p1,p2,n1),q2 = crossover(p2,p1,n1) as Individual of
  S;
  crossover(q1,q2,n2) is Individual of S;
  hence thesis;
end;
