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theory List_HoTT imports MLTT.List Nat begin section \<open>Length\<close> definition [implicit]: "len \<equiv> ListRec {} Nat 0 (fn _ _ rec. suc rec)" experiment begin Lemma "len [] \<equiv> ?n" by (subst comp; typechk?) Lemma "len [0, suc 0, suc (suc 0)] \<equiv> ?n" by (subst comp; typechk?)+ end end