"Neither Bush nor Blair are liars" can be written in two equivalent ways:
$$\lnot (p\lor q) \equiv \lnot p \land \lnot q$$
"Not both Bush and Blair are liars"
$$\lnot (p\land q) = \lnot p \lor \lnot q$$
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$\lnot(p\land q)$ means "Not both (p and q)." This means that that either $\lnot p$ or $\lnot$ q.
$\lnot(p \lor q)$ means it's not the case that (either p holds or q holds), i.e. "neither p nor q," This is equivalent, as noted above, to $\lnot$ p