If L, L1 and L2 are languages, then

- L1 L2 is a language.
- L1 L2 is a language.
- L1 - L2 is a language.
- -L = - L, the complement of L, is a language.

- L1 L2, the catenation of L1 and L2, is a language.

(The strings of L1 L2 are strings that have a word of L1 as a prefix and a word of L2 as a suffix.) - L, the catenation
of L with itself
*n*times, is a language. - L =
L
L LL
LLL LLLL ..., the
*star closure*of L, is a language. - L = L
L LL
LLL LLLL ..., the
*positive closure*of L, is a language.

Copyright © 1996 by David Matuszek

Last modified Jan 29, 1996