forward_list<T> listCopy(forward_list<T> L, forward_list<T> &P){
//concatenate L - in reverse - to the back of P
forward_list<T> temp;
while(!L.empty()){
temp.push_front(L.front());
L.pop_front();
}
P.reverse();
while(!P.empty()){
temp.push_front(P.front());
P.pop_front();
}
P = temp;
return P;
}
