For the field F2\mathbb F_2 is the quotient Z/2Z\mathbb Z/2\mathbb Z, with residue-class addition and multiplication.

Operations and maps

Every nonzero residue has an inverse because 2 is prime. A unit-preserving field endomorphism fixes 11, hence every sum of copies of 11, and is therefore the identity. The zero map is allowed as a nonunital ring map, but never as a field map.

Underlying groups

Its additive group is cyclic of order 22; its nonzero elements form a separate multiplicative group of order 2−12-1. These group structures must be selected explicitly before taking group Hom-sets.