regular language

context-free language

context-sensitive language

recursive enumeration language

Designing computers

Designing compilers

Both 1) Designing computers and 2) Designing compilers

Developing computers

xw * y + xw * yx + ywx

xwy + xw * xy + ywx

xw * y + xw x yx + ywx

xw xy + xww * y + ywx

Recursive languages are closed under complementation.

If a language and its complement are both regular, the language is recursive

Set of recursively enumerable language is closed under union

All of these

Any regular language has an equivalent context-free grammar.

Some non-regular languages can’t be generated by any context-free grammar

Intersection of context free language and a regular language is always context-free

All languages can be generated by context- free grammar