# Creating PDA for {xy such that |x|=|y| and x ≠ y} [duplicate]

I'm trying to create a PDA for $\{xy \mid |x|=|y| \text{ and } x \ne y\}$ over the alphabet $\Sigma = \{a, b\}$. But I don't know how the PDA will know if the two strings $x$ and $y$ are not equal. Please help me create this PDA step by step.
• Use nondeterminism. Try to guess the position $i$ where $x$ and $y$ differ. You have to verify your guess. Use the stack to count to position $i$. – A.Schulz Nov 18 '13 at 15:13
• This language is context-free! and A.Schultz has a good hint. Do not try to find the middle of the word, just guess position $i$. (I stress this as people are presently trying to prove the contrary in the answers.) The question is more or less a duplicate of 16753 and 307 – Hendrik Jan Nov 18 '13 at 20:46