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
  crossover(p1,p2,0,0,0,0,0)=p2
proof
  crossover(p1,p2,0,0,0,0,0) =crossover(crossover(p1,p2,0,0,0,0),p2,0) by Th32;
  hence thesis by Th4;
end;
