# Proving a bipartite graph is never factor-critical

A graph is called to be factor-critical if $G-v$ has a perfect matching for any vertex $v$ of $G$. Prove that a bipartite graph is never factor-critical.

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Let's suppose that $G$ is bipartite, then I guess just let its two color classes consist of $m$ and $n$ vertices with the property such that $m\leq n$.
There's no way we can omit any vertex from the color class that's with $m$ elements so that resulting graph has a perfect matching.
$\therefore$We would get a bipartite graph with two color classes of different size.
Another question, how to prove that $G$ is factor-critical if and only if $G$ has an odd number of vertices and $c_o (G-S)\leq |S|$ for all nonempty set $S$ of vertices –  user68067 Mar 22 '13 at 20:57