Database
CLASSICAL FIRST-ORDER LOGIC WITH EQUALITY
Propositional calculus
Logical conjunction
pm4.65
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Metamath Proof Explorer
Ascii
Structured
Theorem
pm4.65
Description:
Theorem *4.65 of
WhiteheadRussell
p. 120.
(Contributed by
NM
, 3-Jan-2005)
Ref
Expression
Assertion
pm4.65
⊢
( ¬ ( ¬
𝜑
→
𝜓
) ↔ ( ¬
𝜑
∧ ¬
𝜓
) )
Proof
Step
Hyp
Ref
Expression
1
pm4.61
⊢
( ¬ ( ¬
𝜑
→
𝜓
) ↔ ( ¬
𝜑
∧ ¬
𝜓
) )