New answers tagged type-systems
3
$\newcommand{\Alg}{\mathsf{Alg}\ }$
$\newcommand{\NatF}{\mathsf{NatF}\ }$
$\newcommand{\Nat}{\mathsf{Nat}}$
$\newcommand{\map}{\mathrm{map}\ }$
$\newcommand{\Z}{\mathrm{Z}}$
$\newcommand{\S}{\mathrm{S}}$
I don't think this is an actual counter-example.
Parametricity implies:
$$∀(α : \Alg \NatF t) (g : r → t)(x : \NatF r). \\
α\ [r]\ g\ x = α\ [t]\ (λx.x)\ (\...
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