Point.lift_y: def of bend-collections@1.0.0.0
Import: import bend-collections@1.0.0.0/src/crypto/secp256k1/point.bend as Point
Lines 165-167 of bend-collections@1.0.0.0/src/crypto/secp256k1/point.bend: https://jend.leeeet.dev/read.txt?path=bend-collections@1.0.0.0/src/crypto/secp256k1/point.bend&start_line=165&end_line=167

import Base
import bend-collections@1.0.0.0/src/crypto/secp256k1/field.bend as F

# the square root of x^3 + 7 with the given parity, if x^3 + 7 is a square
def lift_y(+y: List<&2, Nat>, +par: Nat) -> List<&2, Nat>:
  F.select(Nat.sub(Nat.add(F.parity(y), par), Nat.mul(Nat.mul(F.parity(y), par), 2n)), F.neg(y), y)

Uses (8):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  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.mul
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.sub
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/src/crypto/secp256k1/field.bend&name=neg
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/src/crypto/secp256k1/field.bend&name=parity
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/src/crypto/secp256k1/field.bend&name=select