# Pastebin BGjF9Hn6
ghci> :t let k :: a %1-> b -> a; k a b = a in k
let k :: a %1-> b -> a; k a b = a in k :: a %1 -> b -> a
ghci> :t let bad_k :: a -> b %1-> a; bad_k a b = a in bad_k

<interactive>:1:37: error:
    • Couldn't match type ‘'Many’ with ‘'One’
        arising from multiplicity of ‘b’
    • In an equation for ‘bad_k’: bad_k a b = a
      In the expression:
        let
          bad_k :: a -> b %1 -> a
          bad_k a b = a
        in bad_k