1/1: Building arity (arity.idr)
arity.idr:4:16--4:21:While processing right hand side of foo at arity.idr:4:1--7:1:
When unifying (1 _ : Nat) -> MyN and MyN
Mismatch between:
	(1 _ : Nat) -> MyN
and
	MyN
at:
4	foo x y = case MkN x of
	               ^^^^^