Metamath Proof Explorer


Theorem frege106

Description: Whatever follows X in the R -sequence belongs to the R -sequence beginning with X . Proposition 106 of Frege1879 p. 73. (Contributed by RP, 7-Jul-2020) (Proof modification is discouraged.)

Ref Expression
Hypothesis frege103.z Z V
Assertion frege106 X t+ R Z X t+ R I Z

Proof

Step Hyp Ref Expression
1 frege103.z Z V
2 1 frege105 ¬ X t+ R Z Z = X X t+ R I Z
3 frege37 ¬ X t+ R Z Z = X X t+ R I Z X t+ R Z X t+ R I Z
4 2 3 ax-mp X t+ R Z X t+ R I Z