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 Th4:
  crossover(p1,p2,0) = p2
proof
  crossover(p1,p2,0) = p2/^0 by FINSEQ_1:34
    .= p2 by FINSEQ_5:28;
  hence thesis;
end;
