rem: r = eval2 ();
add: r = eval2 (evaluate & ~ null (l));
context: eval1 (void){  VALUE *l;  VALUE *r;#ifdef EVAL_TRACE  trace ("eval1");#endif  l = eval2 ();  while (1)    {      if (nextarg ("&"))	{	  r = eval2 ();	  if (null (l) || null (r))	    {	      freev (l);	      freev (r);	      l = int_value (0);	    }	  else	    freev (r);	}      else	return l;    }}