code: func (ss *saveSet) Contains(t *ast.Term, b *bindings) bool {
  	if ss != nil {
  		for el := ss.l.Back(); el != nil; el = el.Prev() {
  			if el.Value.(*saveSetElem).Contains(t, b) {
  				return true
  			}
  		}
  	}
  	return false
  }
docs: // Contains returns true if the term t is contained in the save set. Non-var and
  // non-ref terms are never contained. Ref terms are contained if they share a
  // prefix with a ref that was added (in either direction).