conjunctionLogic & Mathematics
If and only if.
- Let the letter ‘M’ represent this operator, and add to the axioms of classical propositional logic the modal axiom M (p v q) iff Mp v Mq.
- The truth conditions for negation are: A is true iff A is not true.
- Let us say that I could have rendered a proposition false in the weak sense iff I was able to do something such that, if I did it, the proposition would have been falsified (though not necessarily by my act, or by any event caused by my act).
1950s: arbitrary extension of if.
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