List.mem: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 703-705 of bend-mathlib@0.8.1.0/list.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/list.bend&start_line=703&end_line=705

import Base

# Membership in a list, as a reusable proposition.
def mem(~A: Data, ~eq: A -> A -> Bool, +x: A, xs: List<&2, A>) -> Data:
  {List.contains(~A, ~eq, xs, x) == True{} : Bool}

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.contains