„Elsőrendű logika” változatai közötti eltérés

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# '''Inductive Clause I:''' If φ is a ''wff'', then ¬ φ is a ''wff''.
# '''Inductive Clause II:''' If &phi; and &psi; are ''wff''s, then <math>(\phi \wedge \psi)</math>, <math>(\phi \vee \psi)</math>, (&phi; &rarr; &psi;), (&phi; &harr; &psi;) are ''wff''s.
# '''Inductive Clause III:''' If &phi; is a ''wff'' containing a free instance of variable ''x'', then <math> \forall x \, \varphi </math> and <math> \exists x \, \varphi </math> are ''wff''s. (Then any instance of ''x'' is said to be [[binding|bound]] &mdash; not free &mdash; in <math> \forall x \, \varphi </math> and <math> \exists x \, \varphi </math>.)
# '''Closure Clause:''' Nothing else is a ''wff''.
 
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