Reversal of a language :
The reversal of a language L, denoted as
, is defined as: 
.
The reversal of a language L, denoted as
, is defined as: .
Example :
-
Let L = { 0, 11, 01, 011 }. Then = { 0, 11, 10, 110 }.
-
Let L = {
| n is an integer }. Then = { | n is an integer }.
Language concatenation : The concatenation of languages 
and 
is defined as
= { xy | 
and 
}.
Example : { a, ab }{ b, ba } = { ab, aba, abb, abba }.