import logic data.prod set_option pp.notation false inductive C [class] (A : Type) := mk : A → C A definition val {A : Type} (c : C A) : A := C.rec (λa, a) c constant magic (A : Type) : A definition C_magic [instance] [priority std.priority.max] (A : Type) : C A := C.mk (magic A) definition C_prop [instance] : C Prop := C.mk true definition C_prod [instance] {A B : Type} (Ha : C A) (Hb : C B) : C (prod A B) := C.mk (pair (val Ha) (val Hb)) -- C_magic will be used because it has max priority definition test : C (prod Prop Prop) := _ eval test