BY Draconis stars are of spectral class K or M and vary by less than 0.5 magnitudes (70% change in luminosity).

It would include the stars shining down on populated planets, certainly, and probably every star of spectral class K and brighter.

One can easily see that any class K which is an age of some structure satisfies the following three conditions:

Within any giant luminosity class, the cooler stars (spectral class K, M, S, and C) are called red giants.

The second companion is an orange (class K) sixth-magnitude star, that is less massive and of lesser luminosity than the sun.

The PRR assigned class K to the 4-6-2 "Pacific" type.

"This information corresponds to the same sort of signal bleed we'd detect from broadcasts coming off a planetary civilization with class K technological development or better."

A quasivariety is a class K of algebras with a specified signature satisfying any of the following equivalent conditions.

The class K of all infinite σ-structures is elementary.

The class K of all finite σ-structures is not elementary, because (as shown above) its complement is elementary but not basic elementary.