Theorem frege124

Description: If X is a result of an application of the single-valued procedure R to Y and if M follows Y in the R -sequence, then M belongs to the R -sequence beginning with X . Proposition 124 of Frege1879 p. 80. (Contributed by RP, 8-Jul-2020) (Proof modification is discouraged.)

	Ref	Expression
Hypotheses	frege123.x	⊢ 𝑋 ∈ 𝑈
	frege123.y	⊢ 𝑌 ∈ 𝑉
	frege124.m	⊢ 𝑀 ∈ 𝑊
	frege124.r	⊢ 𝑅 ∈ 𝑆
Assertion	frege124	⊢ ( Fun ◡ ◡ 𝑅 → ( 𝑌 𝑅 𝑋 → ( 𝑌 ( t+ ‘ 𝑅 ) 𝑀 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑀 ) ) )

Proof

Step	Hyp	Ref	Expression
1		frege123.x	⊢ 𝑋 ∈ 𝑈
2		frege123.y	⊢ 𝑌 ∈ 𝑉
3		frege124.m	⊢ 𝑀 ∈ 𝑊
4		frege124.r	⊢ 𝑅 ∈ 𝑆
5	1 2 3 4	frege110	⊢ ( ∀ 𝑎 ( 𝑌 𝑅 𝑎 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑎 ) → ( 𝑌 ( t+ ‘ 𝑅 ) 𝑀 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑀 ) )
6	1 2	frege123	⊢ ( ( ∀ 𝑎 ( 𝑌 𝑅 𝑎 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑎 ) → ( 𝑌 ( t+ ‘ 𝑅 ) 𝑀 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑀 ) ) → ( Fun ◡ ◡ 𝑅 → ( 𝑌 𝑅 𝑋 → ( 𝑌 ( t+ ‘ 𝑅 ) 𝑀 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑀 ) ) ) )
7	5 6	ax-mp	⊢ ( Fun ◡ ◡ 𝑅 → ( 𝑌 𝑅 𝑋 → ( 𝑌 ( t+ ‘ 𝑅 ) 𝑀 → 𝑋 ( ( t+ ‘ 𝑅 ) ∪ I ) 𝑀 ) ) )