Schnorr.lift_if: def of bend-collections@1.0.0.0
Import: import bend-collections@1.0.0.0/spec/crypto/secp256k1/schnorr.bend as Schnorr
Lines 57-62 of bend-collections@1.0.0.0/spec/crypto/secp256k1/schnorr.bend: https://jend.leeeet.dev/read.txt?path=bend-collections@1.0.0.0/spec/crypto/secp256k1/schnorr.bend&start_line=57&end_line=62

import Base
import bend-collections@1.0.0.0/spec/crypto/secp256k1/curve.bend as CV

# lift_x(x): the point with x-coordinate x and even y, if x < p and
# x^3 + 7 is a square
def lift_if(+one: Nat, +x: Nat, ok: Bool) -> Maybe<&2, CV.SPoint>:
  match ok:
    case True{}: CV.decompress(p(one), x, 0n)
    case False{}: None{}

Uses (6):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  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=bend-collections@1.0.0.0/spec/crypto/secp256k1/curve.bend&name=SPoint
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/spec/crypto/secp256k1/curve.bend&name=decompress
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/spec/crypto/secp256k1/schnorr.bend&name=p