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BfContraPosImpDist
⊢
(
¬
g
⊃ ¬
f
)
⊃
(
f
)
⊃
(
g
)
BfContraPosImpDist
Proof:
1
(
¬
g
⊃ ¬
f
)
⊃
(
¬
g
)
⊃
(
¬
f
)
BfImpDfImpDf
2
(
¬
g
⊃ ¬
f
)
⊃
(
¬
¬
f
)
⊃
(
¬
¬
g
)
1
,
Prop
3
(
¬
g
⊃ ¬
f
)
⊃
(
f
)
⊃
(
g
)
2
,
def. of
qed
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2024-08-03
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