The Bordalo order on a commutative ring
If is a commutative ring with identity and is defined by letting mean or , then is a partially ordered ring. Necessary and sufficient conditions on are given for to be a lattice, and conditions are given for it to be modular or distributive. The results are applied to the rings of integers mod for . In particular, if is reduced, then is a lattice iff is a weak Baer ring, and is a distributive lattice iff is a Boolean ring, , , or a four element field.