Perm.evens: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/perm.bend as Perm
Lines 189-199 of bend-mathlib@0.8.1.0/perm.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/perm.bend&start_line=189&end_line=199

import Base

# The elements of a list at even positions (0, 2, 4, ...).
def evens(-A: Data, xs: List<&2, A>) -> List<&2, A>:
  match xs:
    case Nil{}:
      Nil{}
    case +x <> r:
      match r:
        case Nil{}:
          x <> Nil{}
        case +y <> t:
          x <> evens(A, t)

Uses (1):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List