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BiContraPosImpDist
⊢
(
¬
g
⊃ ¬
f
)
⊃
(
f
)
⊃
(
g
)
BiContraPosImpDist
Proof:
1
⊢
(
¬
g
⊃ ¬
f
)
⊃
(
¬
g
)
⊃
(
¬
f
)
BiImpDiImpDi
2
⊢
(
¬
g
⊃ ¬
f
)
⊃
(
¬
¬
f
)
⊃
(
¬
¬
g
)
1
,
Prop
3
⊢
(
¬
g
⊃ ¬
f
)
⊃
(
f
)
⊃
(
g
)
2
,
def. of
qed
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2023-09-12
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