get rid of redundant code in is_closed function
get rid of redundant code in is_closed function

ktakashi/picrin,omasanori/picrin,dcurrie/picrin,ktakashi/picrin,dcurrie/picrin,leavesbnw/picrin,ktakashi/picrin,picrin-scheme/picrin,leavesbnw/picrin,koba-e964/picrin,leavesbnw/picrin,koba-e964/picrin,picrin-scheme/picrin,koba-e964/picrin,omasanori/picrin