Precisely Unless

If A is true precisely unless B, then B implies not-A and not-B implies A. J. H. Conway has suggested the term "unlesss" for this state of affairs, by analogy with iff.

See also

At Least One, Exactly One, Iff, Unless

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Cite this as:

Weisstein, Eric W. "Precisely Unless." From MathWorld--A Wolfram Web Resource.

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