Is Not Necessarily Equal To

At lunch at Nuffield I was just asking MM about some math notation I'd like: a symbol for "is not necessarily equal to". For example, and economics paper might show the following:

Proposition: Stocks with equal risks might or might not have the same returns. In the model's notation, x IS NOT NECESSARILY EQUAL TO y.

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I can't say x \neq y there, because maybe x=y, maybe not, depending on the parameter values.

If anybody knows of such a symbol, please let me know. In fact, just a symbol for IS NOT NECESSARILY might be useful, since we could combine it with other symbols, e.g.

x IS NOT NECESSARILY = y

Horse heights ARE NOT NECESSARILY > cow heights

The biased estimator IS NOT NECESSARILY \sim N(0,1).

OCTOBER 7. Stimulated by a comment below: The modal logic symbols might work well. Wikipedia's "Modal logic" says: "The basic modal operators are usually written (or L) for Necessarily and (or M) for Possibly."

Maybe I could say " x ≠ y" for "x is not necessarily equal to y".