The morphism
const Z4 = Chalkboard.abal.group(Chalkboard.abal.Z(4), (a, b) => (a + b) % 4, 0, (a) => (4 - a) % 4);
const Z2 = Chalkboard.abal.group(Chalkboard.abal.Z(2), (a, b) => (a + b) % 2, 0, (a) => a);
const parity = Chalkboard.abal.homomorphism(Z4, Z2, (x) => x % 2);
const valid = Chalkboard.abal.isSurjective(parity); // Returns true
Checks if a morphism is surjective.