Metamath Proof Explorer


Theorem 19.31

Description: Theorem 19.31 of Margaris p. 90. See 19.31v for a version requiring fewer axioms. (Contributed by NM, 14-May-1993)

Ref Expression
Hypothesis 19.31.1 xψ
Assertion 19.31 xφψxφψ

Proof

Step Hyp Ref Expression
1 19.31.1 xψ
2 1 19.32 xψφψxφ
3 orcom φψψφ
4 3 albii xφψxψφ
5 orcom xφψψxφ
6 2 4 5 3bitr4i xφψxφψ