what is language of repeat(L) = {ww | w  L} ?I know it {ww | w  (a,b)*} is context sensitive language. here , what is meant by repeat(L) ?  Can you explain it ? It is not a homework question . 
what is language of repeat(L) = {ww | w  L}?
regular languages;regular expressions;context sensitive
$repeat(\cdot)$ is an operator on languages. It takes as an input a language $L$, and outputs a language defined by $\{ xx \mid x \in L\}$. That is, for any word $x\in L$ the string $xx$ will be in the output language $repeat(L)$.A Few examples:$L=\{ 0,00, 11\}$  =>  $repeat(L) = \{ 00,0000,1111\}$$L=\{ \}$   => $repeat(L) = \{ \}$$L=\Sigma^*=\{\epsilon,0,1,00,01,10,11,...\}$ => $repeat(L)= \{\epsilon, 00,11,0000,0101,1010,1111,...\}$