Hi, the case-identity transformation is case e of pat1 -> pat1 ===> e ... patn -> patn It's performed in SimplUtils.mkCase1. My (very special) question is: How do you ensure, that there's a case-alternative for every constructor of the type of e? Otherwise you could transform case e of {True -> True} ===> True, if e is of type Bool, but that't not correct if e is False. Maybe you add a default-alternative DEFAULT -> error ... ? Thanks, David