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Theorem rnlem 882
Description: Lemma used in construction of real numbers. (Contributed by NM, 4-Sep-1995.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)
Assertion
Ref Expression
rnlem (((φ ψ) (χ θ)) ↔ (((φ χ) (ψ θ)) ((φ θ) (ψ χ))))

Proof of Theorem rnlem
StepHypRef Expression
1 an4 520 . . . 4 (((φ ψ) (χ θ)) ↔ ((φ χ) (ψ θ)))
21biimpi 113 . . 3 (((φ ψ) (χ θ)) → ((φ χ) (ψ θ)))
3 an42 521 . . . 4 (((φ θ) (ψ χ)) ↔ ((φ ψ) (χ θ)))
43biimpri 124 . . 3 (((φ ψ) (χ θ)) → ((φ θ) (ψ χ)))
52, 4jca 290 . 2 (((φ ψ) (χ θ)) → (((φ χ) (ψ θ)) ((φ θ) (ψ χ))))
63biimpi 113 . . 3 (((φ θ) (ψ χ)) → ((φ ψ) (χ θ)))
76adantl 262 . 2 ((((φ χ) (ψ θ)) ((φ θ) (ψ χ))) → ((φ ψ) (χ θ)))
85, 7impbii 117 1 (((φ ψ) (χ θ)) ↔ (((φ χ) (ψ θ)) ((φ θ) (ψ χ))))
Colors of variables: wff set class
Syntax hints:   wa 97  wb 98
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101
This theorem depends on definitions:  df-bi 110
This theorem is referenced by: (None)
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