We use an inclusion-exclusion argument, and express 
as the union of the following six languages.
The sum of the polynomials of these 6 languages is 
The sum of the polynomials describing these 15 languages
is 
The sum of the polynomials describing these 20 languages
is 
The sum of the polynomials describing these 15 languages
is 
The sum of the polynomials describing these 6 languages
is 
The polynomial of this language
is 
The polynomial describing the language 
is therefore
The polynomial describing the (inaccessible) language 
is therefore
