#include "tree.h"

  
  tree make_empty_tree(){
    return NULL;
  }
  int is_empty(tree t){
    return t==NULL;
  }
  int is_leaf(tree t){
    return is_empty(t.next);//<=>t.val=='\0'
  }
  int is_end(tree t){
    return isIn_list(t.next,'\0');
  }