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[Benedikt Ahrens <benedikt.ahrens AT irit.fr>]

Hello,

of the two pieces of code below, the first one is accepted whereas the 
second one does not typecheck; the line "Check..." fails (in Coq8.4pl3).

Could someone explain why? Is this a necessary restriction of the 
coercion mechanism?

Thanks a lot in advance.
Benedikt

=== 1 ===
Definition UU := Type.
Definition PointedUU := sigT (fun A : UU => A).
Definition carrier (C : PointedUU) : Type := @projT1 _ _ C.
Coercion carrier : PointedUU >-> Sortclass.
Check (fun C : PointedUU => fun c : C => c).
=========

=== 2 ===
Definition UU := Type.
Definition PointedUU := sigT (fun A : UU => A).
Definition carrier (C : PointedUU) := @projT1 _ _ C.
Coercion carrier : PointedUU >-> UU.
Check (fun C : PointedUU => fun c : C => c). (* fails *)
=========