the mathematical symbol

[Tuukka Toivonen]

I need the mathematical symbol that is a combination of \neq and \equiv,
that is, the the symbol "=" but with three horizontal lines like in
        a = b (mod p)
AND that symbol logically inverted, ie. a slash overdrawn like in
        a 'does not belong in the same residue class than' b (mod p)

or graphically,

              /
        -------
            /
        -------
          /
        -------
        /

This is not very important, so please don't waste hours of your precious
time just to help me :)
A general way how to get two symbols overstriken would be nice.