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### 4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / a. Symbols of PL

#### [main symbols used for propositional and further logics]

10 ideas
 22435 The logician's '→' does not mean the English if-then [Quine]
 9511 We write the conditional 'if P (antecedent) then Q (consequent)' as P→Q [Lemmon]
 9512 We write the 'negation' of P (not-P) as ¬ [Lemmon]
 9508 The sign |- may be read as 'therefore' [Lemmon]
 9510 That proposition that either P or Q is their 'disjunction', written P∨Q [Lemmon]
 9509 That proposition that both P and Q is their 'conjunction', written P∧Q [Lemmon]
 9513 We write 'P if and only if Q' as P↔Q; it is also P iff Q, or (P→Q)∧(Q→P) [Lemmon]
 9514 If A and B are 'interderivable' from one another we may write A -||- B [Lemmon]
 12005 The symbol 'ι' forms definite descriptions; (ιx)F(x) says 'the x which is such that F(x)' [Forbes,G]
 7799 Proposition logic has definitions for its three operators: or, and, and identical [Girle]