English edit

Etymology edit

From regular + open; apparently a backformation from regular open set.

Adjective edit

regular open (not comparable)

  1. (rare, mathematics, of a set) Being the interior of its closure.
    The set (0,1)∪(1,2) is open, but is not regular open, because its closure is [0,2], so the interior of its closure is (0,2).

See also edit