code: void pop( Env global ) {
      assert _sp > _display[_tod]; // Do not over-pop current scope
      _sp--;
      _fcn[_sp]=global.subRef(_fcn[_sp]);
      _ary[_sp]=global.subRef(_ary[_sp],_key[_sp]);
      assert _sp==0 || _ary[0]==null || check_refcnt(_ary[0].anyVec());
    }
docs: (to avoid dangling pointers stretching lifetimes).