Namely: For a given A != B, (!A or !B) == !(A && B), which will always be true for any single value.

ow.

You attached two conditions to (!A or !B) == !(A && B), but it's always true.

You refer some non-existent "single value" because you meant to talk about (V != A) or (V != B).

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I believe you meant:

(A or B)
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is equivalent to

!(!A and !B)
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Because of that,

(V != A) or (V != B)
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is equivalent to

!( (V == A) and (V == B) )
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If A != B, the "and" is obviously false (since V can't have two different values at the same time), and the whole statement is therefore true.