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Mirrors > Home > MPE Home > Th. List > pm5.21ni | Structured version Visualization version GIF version |
Description: Two propositions implying a false one are equivalent. (Contributed by NM, 16-Feb-1996.) (Proof shortened by Wolf Lammen, 19-May-2013.) |
Ref | Expression |
---|---|
pm5.21ni.1 | ⊢ (𝜑 → 𝜓) |
pm5.21ni.2 | ⊢ (𝜒 → 𝜓) |
Ref | Expression |
---|---|
pm5.21ni | ⊢ (¬ 𝜓 → (𝜑 ↔ 𝜒)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | pm5.21ni.1 | . . 3 ⊢ (𝜑 → 𝜓) | |
2 | 1 | con3i 154 | . 2 ⊢ (¬ 𝜓 → ¬ 𝜑) |
3 | pm5.21ni.2 | . . 3 ⊢ (𝜒 → 𝜓) | |
4 | 3 | con3i 154 | . 2 ⊢ (¬ 𝜓 → ¬ 𝜒) |
5 | 2, 4 | 2falsed 375 | 1 ⊢ (¬ 𝜓 → (𝜑 ↔ 𝜒)) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 → wi 4 ↔ wb 205 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 |
This theorem depends on definitions: df-bi 206 |
This theorem is referenced by: pm5.21nii 377 norbi 883 pm5.54 1014 niabn 1017 ab0w 4372 csbprc 4405 ralf0 4512 ordsssuc2 6454 ndmovord 7599 ordsucelsuc 7812 brdomg 8954 brdomgOLD 8955 suppeqfsuppbi 9379 funsnfsupp 9389 r1pw 9842 r1pwALT 9843 elixx3g 13341 elfz2 13495 bifald 37258 areaquad 42267 |
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