Conjunction
(logic, mathematics) Is equivalent to; implies and is implied by; is true and false in the same cases as.
A rectangle is a square if and only if all four of its sides have the same length.
An integer is even if and only if its square is also even.
(by extension, informal) If, with added intensity
Source: en.wiktionary.orgYou are rich if and only if money you refuse tastes better than money you accept. Nassim Nicholas Taleb
Each community must win and hold the voluntary adherence of its members. No pattern is imposed on everyone, and the result will be one pattern if and only if everyone voluntarily chooses to live in accordance with that pattern of community. Robert Nozick
You have a real life if and only if you do not compete with anyone in any of your pursuits. Nassim Nicholas Taleb
You exist if and only if you are free to do things without a visible objective, with no justification and, above all, outside the dictatorship of someone else's narrative. Nassim Nicholas Taleb
You can overcome anything, if and only if you love something enough. Lionel Messi
A characterization of finite dimensionality is that a Hausdorff TVS is locally compact if and only if it is finite-dimensional (therefore isomorphic to some Euclidean space). Source: Internet