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Mirrors > Home > MPE Home > Th. List > alex | Structured version Visualization version GIF version |
Description: Universal quantifier in terms of existential quantifier and negation. Dual of df-ex 1781. See also the dual pair alnex 1782 / exnal 1827. Theorem 19.6 of [Margaris] p. 89. (Contributed by NM, 12-Mar-1993.) |
Ref | Expression |
---|---|
alex | ⊢ (∀𝑥𝜑 ↔ ¬ ∃𝑥 ¬ 𝜑) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | notnotb 317 | . . 3 ⊢ (𝜑 ↔ ¬ ¬ 𝜑) | |
2 | 1 | albii 1820 | . 2 ⊢ (∀𝑥𝜑 ↔ ∀𝑥 ¬ ¬ 𝜑) |
3 | alnex 1782 | . 2 ⊢ (∀𝑥 ¬ ¬ 𝜑 ↔ ¬ ∃𝑥 ¬ 𝜑) | |
4 | 2, 3 | bitri 277 | 1 ⊢ (∀𝑥𝜑 ↔ ¬ ∃𝑥 ¬ 𝜑) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 ↔ wb 208 ∀wal 1535 ∃wex 1780 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 |
This theorem depends on definitions: df-bi 209 df-ex 1781 |
This theorem is referenced by: exnal 1827 2nalexn 1828 alimex 1831 emptyal 1909 19.3vOLD 1989 nfa1 2155 sp 2182 exists2 2747 pm10.253 40714 vk15.4j 40882 vk15.4jVD 41268 |
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