i) The last sentence on page 573 of Cohen refers to the Venn diagram on page 574. Also wikipedia refers to the Chomsky Hierarchy with the lower (inner) levels as proper subsets of the higher. See

http://en.wikipedia.org/wiki/Regular_language
ii) Why I say 'non-regular languages are a sub set of regular languages. (example on page 193)'?

On the top of page 188 in Cohen, that is what he says.

(a

^{n}b

^{n} is a subset of a*b* for n >= 0).

With the example on pg 193. The intersection of a*b* and EQUAL is a

^{n}b

^{n}, which is non-regular, because EQUAL is non-regular. So a

^{n}b

^{n} is a subset of regular and non-regular.

iii) Also in Cohen, question 15 of chapter 10 asks for examples of languages:

a*b* = a*b* + a

^{n}b

^{n} (regular = regular + non-regular) (+=union [and])

and

let R = {bbaa, ba} and N = b

^{n}a

^{n}, then N=R+N (non-regular = regular + non-regular) (+=union [and])

iv)

Quote

**becked**

The diagram on p. 574 illustrates classes of languages. A regular language can be generated by a regular expression, and it will also be accepted by a PDA (context free) and also by a Turing Machine (recursive) as described in COS301.

So regular languages are in other classes of languages?

If the regular class consists of regular languages, then are the other classes non-regular?

- So, to me, non-regular languages are a subset of regular languages. From (ii) and (iii) above.

- If regular languages are in other classes (from (iv)), then regular languages will be a subset of non-regular languages. From (i), (iii) above.

- A language is either regular or non-regular.

Ummmm. Well!!! Yes!!!!!!!!!!!

I can actually understand this to be true. Surprisingly. Or am I totally mad.