Description: If ph or ps takes place, then ps or ph takes place. Identical to con1 . Proposition 33 of Frege1879 p. 44. (Contributed by RP, 24-Dec-2019) (Proof modification is discouraged.)
Ref | Expression | ||
---|---|---|---|
Assertion | frege33 | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ax-frege28 | |
|
2 | frege32 | |
|
3 | 1 2 | ax-mp | |