#   type (_, _) eq = Refl : ('a, 'a) eq
# val cast : ('a, 'b) eq -> 'a -> 'b = <fun>
#           Characters 53-78:
    let rec (p : (int, a) eq) = match p with Refl -> Refl in
                                ^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This kind of expression is not allowed as right-hand side of `let rec'
#