NatOrder.step: def of bend-kit-collections@0.1.4.1
Import: import bend-kit-collections@0.1.4.1/nat_order.bend as NatOrder
Lines 41-44 of bend-kit-collections@0.1.4.1/nat_order.bend: https://jend.leeeet.dev/read.txt?path=bend-kit-collections@0.1.4.1/nat_order.bend&start_line=41&end_line=44

import Base
import bend-mathlib@0.7.4.0/nat.bend as MNat

def step(+a: Nat, +b: Nat, +c: Nat, +d: Nat, -x: Nat, -y: Nat, e1: {Nat.add(a, c) == x : Nat},
  e2: {Nat.add(b, d) == y : Nat}) -> {Nat.add(Nat.add(a, b), Nat.add(c, d)) == Nat.add(x, y) : Nat}:
  tr(Nat.add(Nat.add(a, b), Nat.add(c, d)), Nat.add(Nat.add(a, c), Nat.add(b, d)), Nat.add(x, y),
    MNat.add_add_add_comm(a, b, c, d), cong_add(Nat.add(a, c), x, Nat.add(b, d), y, e1, e2))

Uses (5):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.add
  https://jend.leeeet.dev/definition.txt?path=bend-kit-collections@0.1.4.1/nat_order.bend&name=cong_add
  https://jend.leeeet.dev/definition.txt?path=bend-kit-collections@0.1.4.1/nat_order.bend&name=tr
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/nat.bend&name=add_add_add_comm