Nat.pred_double: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/proofs/lib/nat.bend as Nat
Lines 467-474 of bend-collections-laws-crypto@1.0.0.0/proofs/lib/nat.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/proofs/lib/nat.bend&start_line=467&end_line=474

import Base
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/logic.bend as L

# pred(2v) == 1 + 2 pred(v) for v >= 1.
def pred_double(+v: Nat, e: {Nat.is_le(1n, v) == True{} : Bool}) -> {Nat.sub(Nat.double(v), 1n) == 1n+Nat.double(Nat.sub(v, 1n)) : Nat}:
  match v:
    case 0n:
      Empty.absurd({Nat.sub(0n, 1n) == 1n+Nat.double(Nat.sub(0n, 1n)) : Nat}, L.false_true(e))
    case 1n+p:
      %Equal.sym(Nat, Nat.sub(p, 0n), p, sub_zero(p)) : {1n+Nat.double(p) == 1n+Nat.double(_) : Nat}
      {==}

Uses (9):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Empty.absurd
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Equal.sym
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.double
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.is_le
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.sub
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/proofs/lib/logic.bend&name=false_true
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/proofs/lib/nat.bend&name=sub_zero