nLab improper ideal

The improper ideal


An ideal is improper if it is the whole thing … whatever thing the ideals are ideals in.


As there are different (but related) kinds of ideal, there are different (but very similar) kinds of improper ideal.

Definition (improper ideal of a ring or other rig)

If RR is a ring or even a rig, then RR is a two-sided ideal of itself, the improper ideal.

Definition (improper ideal of a lattice or other proset)

If LL is a lattice or even a proset, then LL is an ideal of itself, the improper ideal.


The improper ideal contrasts with proper ideals (all of the other ideals).

The improper ideal does not count as a prime ideal or a maximal ideal, because it is too simple to be simple, although it may satisfy careless or naïve definitions of those concepts (which must be required to be proper).

Conversely, sometimes one defines ‘ideal’ to exclude the improper ideal, but this makes the set of all ideals less nice to work with.

Created on August 17, 2012 at 21:20:51. See the history of this page for a list of all contributions to it.