$L = \{ a^ib^j \mid j\neq i \ and \ j\neq2i \ \} $
Is this language a context free language? If yes give a PDA. If no, give a proof.
The pumping lemma for context free languages doesn't seem to work here.
Let $p>1$ be the pumping length. Let the string be divided into five parts according to pumping lemma as $w = uvxyz$.
For any string of the form $a^ib^j \ s.t.$:
$ j\lt i-1$ choose $v=a, \ x=\epsilon, \ y=\epsilon$
$ j\gt 2i+1$ choose $v=\epsilon, \ x=\epsilon, \ y=b$
$ j = i-1$ choose $v=a, \ x=\epsilon, \ y=b$
$ j = 2i+1$ choose $v=a, \ x=\epsilon, \ y=b$
$ j\gt i,\ j\lt 2i $ choose $v=a, \ x=\epsilon, \ y=b$