node BiInsertLeftChild(labeltype l, node i, BinaryTree *Tp){
  if(i==NULL) exit(8); //nije definirana
  if(i->leftchild!=NULL) return LAMBDA;
  i->leftchild->label=l;
  i->leftchild->leftchild=i->leftchild->rightchild=NULL;
  return i->leftchild;
}