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Theorem dflb2s 92
Description: Reverse implication of biconditional definition.
Assertion
Ref Expression
dflb2s (((𝜑𝜓) & (𝜓𝜑)) ⊸ (𝜑𝜓))

Proof of Theorem dflb2s
StepHypRef Expression
1 ax-init 7 . . . . . 6 (~ (𝜑𝜓) ⅋ (𝜑𝜓))
21dfli1 63 . . . . 5 (~ (𝜑𝜓) ⅋ (~ 𝜑𝜓))
32dfli2i 66 . . . 4 ((𝜑𝜓) ⊸ (~ 𝜑𝜓))
43acm1s 84 . . 3 (((𝜑𝜓) & (𝜓𝜑)) ⊸ ((~ 𝜑𝜓) & (𝜓𝜑)))
5 ax-init 7 . . . . . 6 (~ (𝜓𝜑) ⅋ (𝜓𝜑))
65dfli1 63 . . . . 5 (~ (𝜓𝜑) ⅋ (~ 𝜓𝜑))
76dfli2i 66 . . . 4 ((𝜓𝜑) ⊸ (~ 𝜓𝜑))
87acm2s 85 . . 3 (((~ 𝜑𝜓) & (𝜓𝜑)) ⊸ ((~ 𝜑𝜓) & (~ 𝜓𝜑)))
94, 8syl 75 . 2 (((𝜑𝜓) & (𝜓𝜑)) ⊸ ((~ 𝜑𝜓) & (~ 𝜓𝜑)))
10 df-lb 56 . . . 4 ((~ (𝜑𝜓) ⅋ ((~ 𝜑𝜓) & (~ 𝜓𝜑))) & (~ ((~ 𝜑𝜓) & (~ 𝜓𝜑)) ⅋ (𝜑𝜓)))
1110eac2i 40 . . 3 (~ ((~ 𝜑𝜓) & (~ 𝜓𝜑)) ⅋ (𝜑𝜓))
1211dfli2i 66 . 2 (((~ 𝜑𝜓) & (~ 𝜓𝜑)) ⊸ (𝜑𝜓))
139, 12syl 75 1 (((𝜑𝜓) & (𝜓𝜑)) ⊸ (𝜑𝜓))
Colors of variables: wff var nilad
Syntax hints:  wmd 2  ~ wneg 3   & wac 30  wlb 55  wli 61
This theorem was proved from axioms:  ax-ibot 4  ax-ebot 5  ax-cut 6  ax-init 7  ax-mdco 8  ax-mdas 9  ax-iac 32  ax-eac1 33  ax-eac2 34
This theorem depends on definitions:  df-lb 56  df-li 62
This theorem is referenced by:  dflb  93
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