Yes, you can get it all into one statement, but I think that ikegami's answer is much more legible, easier to understand, and thus, easier to maintain.

But based on the order of precedence from ikegami:

if (not B) {
   A 
} else {
   if (E and F) {   
      C and D
   } else {         
      undef
   }
}
[download]

You could use:

( ! B ) ? A : ( ( E and F ) ? ( C and D ) : undef );

or for legibility:

(! B )
  ? A
  :(
    (E and F)
      ? (C and D)
      : undef
  );
[download]

or the completely horrible line noise:

!B?A:E&&F?C&&D:undef;