Commutative pm rings

**Abstract**

We limit the discussion to commutative rings. A ring R is called pm if
each prime ideal lies in only one maximal ideal. The class is limited but
natural as evidenced by examples we give.

We present in detail a beautiful theorem due to DeMarco and Orsatti that
characterizes these rings.

**Thm** The following are equivalent.

- R is pm
- Spec R is normal
- Max R is a retract of Spec R.