List.concat: def of Base
Import: import Base
Lines 939-944 of Base/base.bend: https://jend.leeeet.dev/read.txt?path=Base/base.bend&start_line=939&end_line=944

import Base

def List.concat(a, -A: Kind(a), xss: List<a, List<a, A>>) -> List<a, A>:
  match xss:
    case Nil{}:
      Nil{}
    case h <> t:
      List.append(a, A, h, List.concat(a, A, t))

Uses (2):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.append