On 2011-12-16 12:22, Peter Thiemann wrote: > That's how I understand Conor's suggestion: > a metavariable with an empty type like T(false) > that can never be filled in. As Conor mentions such a metavariable /can/ sometimes be filled in. Simple example: id-⊥ : ⊥ → ⊥ id-⊥ x = x -- /NAD