<sod>  * the [[homomorphism]] φ(L) of ''L''
 * the [[concatenation]] <math>L \circ P</math> of ''L'' and ''P''
 * the [[union (set theory)|union]] <math>L \cup P</math> of ''L'' and ''P''
* the [[intersection]] (with a Regular Language) <math>L \cap D</math> of ''L'' and ''D''
 
Context-Free Languages are not closed under [[complement (complexity)|complement]], [[intersection]], or [[difference]].
 
 ==See also==
 There is a [[pumping lemma]] for context-free languages that gives a necessary condition for a language to be context-free.
 <eod> <sod> * the [[homomorphism]] φ(L) of ''L''
 * the [[concatenation]] <math>L \circ P</math> of ''L'' and ''P''
 * the [[union (set theory)|union]] <math>L \cup P</math> of ''L'' and ''P''
* the [[intersection (set theory)|intersection]] (with a Regular Language) <math>L \cap D</math> of ''L'' and ''D''
 
Context-Free Languages are not closed under [[complement (complexity)|complement]], [[intersection (set theory)|intersection]], or [[difference]].
 
 ==See also==
 There is a [[pumping lemma]] for context-free languages that gives a necessary condition for a language to be context-free.
 <eod>