On Saturday, 7 July 2012 at 16:14:13 UTC, Tobias Pankrath wrote: > Interesting, I thought that PEG ⊂ CFG holds. See section 3.4 of http://bford.info/pub/lang/peg.pdf It contains a simple proof that a non-context-free language (a^n) (b^n) (c^n) can be described with PEG syntax. There are infinitely many such languages.