消除公共前缀的例子 stm→ id stm Stm -id Exp stm→:=Exp stm→id(ExpL)→Stm′→(ExpL) ExpL→Exp ExpL→ Exp ExpL′ ExpL→Exp,ExpL EXpL′→, Exp ExpL′ ExpL′→λStm → id := Exp Stm → id (ExpL) ExpL → Exp ExpL → Exp,ExpL Stm → id Stm Stm → := Exp Stm → ( ExpL ) ExpL → Exp ExpL ExpL → , Exp ExpL ExpL →   消除公共前缀的例子