ProofNum.step_fb: law of lawful-fields@0.1.1.0
Import: import lawful-fields@0.1.1.0/proof_num.bend as ProofNum
Lines 370-379 of lawful-fields@0.1.1.0/proof_num.bend: https://jend.leeeet.dev/read.txt?path=lawful-fields@0.1.1.0/proof_num.bend&start_line=370&end_line=379

import Base

# After a digit, by the overflow test (b).
law step_fb:
  for +acc: U32
  for +x: U32
  for +M: Nat
  for +b: Bool
  for +hm: {Nat.pow(2n, 32n) == M : Nat}
  for +hge: {U32.is_ge(x, 48) == True{} : Bool}
  for +hb: {Nat.is_lt(Nat.add(Nat.mul(U32.to_nat(acc), 10n), Nat.sub(U32.to_nat(x), 48n)), M) == b : Bool}
  Inv(b, NA(acc, x), Some{Nat.add(Nat.mul(U32.to_nat(acc), 10n), Nat.sub(U32.to_nat(x), 48n))}, M)

Uses (18):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Equal.cong
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Equal.sym
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  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=Base/base.bend&name=Nat.is_lt
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.mul
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.pow
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.sub
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Sigma
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.is_ge
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.to_nat
  https://jend.leeeet.dev/definition.txt?path=lawful-arrays@0.1.0.0/proof_base.bend&name=subst
  https://jend.leeeet.dev/definition.txt?path=lawful-fields@0.1.1.0/proof_num.bend&name=Inv
  https://jend.leeeet.dev/definition.txt?path=lawful-fields@0.1.1.0/proof_num.bend&name=NA
  https://jend.leeeet.dev/definition.txt?path=lawful-fields@0.1.1.0/proof_num.bend&name=ena