def List.zip
import Base1028def List.zip(
1029 a, -A: Kind(a), b, -B: Kind(b), xs: List<a, A>, ys: List<b, B>
1030) -> List<&1, A & B>:
1031 match xs ys:
1032 case Nil{} _:
1033 Nil{}
1034 case h <> t Nil{}:
1035 Nil{}
1036 case x <> xt y <> yt:
1037 (x, y) <> List.zip(a, A, b, B, xt, yt)