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

# Precisely Unless

## See also

At Least One, Exactly One, Iff, Unless## Explore with Wolfram|Alpha

## Cite this as:

Weisstein, Eric W. "Precisely Unless."
From *MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/PreciselyUnless.html