1/1: Building Error (Error.idr)
Error: While processing right hand side of wrong. Undefined name ys. 

Error:6:17--6:19
 2 |      Nil : Vect Z a
 3 |      (::) : a -> Vect k a -> Vect (S k) a
 4 | 
 5 | wrong : a -> Vect (S n) a -> Vect (S n) a
 6 | wrong xs = x :: ys
                     ^^