Schnorr.even_b: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/schnorr.bend as Schnorr
Lines 46-50 of bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/schnorr.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/schnorr.bend&start_line=46&end_line=50

import Base
import bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/field.bend as FS

# n - x when y is odd (the key or nonce whose point has even y)
def even_b(+m: Nat, b: Nat, +x: Nat) -> Nat:
  match b:
    case 0n: x
    case 1n+k: FS.mneg(m, x)

Uses (2):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/field.bend&name=mneg