Theorem sbequ 2083

Description: Equality property for substitution, from Tarski's system. Used in proof of Theorem 9.7 in [Megill] p. 449 (p. 16 of the preprint). (Contributed by NM, 14-May-1993.) Revise df-sb 2065. (Revised by BJ, 30-Dec-2020.)

Assertion

Ref	Expression
sbequ	⊢ (𝑥 = 𝑦 → ([𝑥 / 𝑧]𝜑 ↔ [𝑦 / 𝑧]𝜑))

Proof of Theorem sbequ

Dummy variable 𝑢 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		equequ2 2025	. . . 4 ⊢ (𝑥 = 𝑦 → (𝑢 = 𝑥 ↔ 𝑢 = 𝑦))
2	1	imbi1d 341	. . 3 ⊢ (𝑥 = 𝑦 → ((𝑢 = 𝑥 → ∀𝑧(𝑧 = 𝑢 → 𝜑)) ↔ (𝑢 = 𝑦 → ∀𝑧(𝑧 = 𝑢 → 𝜑))))
3	2	albidv 1919	. 2 ⊢ (𝑥 = 𝑦 → (∀𝑢(𝑢 = 𝑥 → ∀𝑧(𝑧 = 𝑢 → 𝜑)) ↔ ∀𝑢(𝑢 = 𝑦 → ∀𝑧(𝑧 = 𝑢 → 𝜑))))
4		df-sb 2065	. 2 ⊢ ([𝑥 / 𝑧]𝜑 ↔ ∀𝑢(𝑢 = 𝑥 → ∀𝑧(𝑧 = 𝑢 → 𝜑)))
5		df-sb 2065	. 2 ⊢ ([𝑦 / 𝑧]𝜑 ↔ ∀𝑢(𝑢 = 𝑦 → ∀𝑧(𝑧 = 𝑢 → 𝜑)))
6	3, 4, 5	3bitr4g 314	1 ⊢ (𝑥 = 𝑦 → ([𝑥 / 𝑧]𝜑 ↔ [𝑦 / 𝑧]𝜑))

Syntax hints:   → wi 4   ↔ wb 206  ∀wal 1535  [wsb 2064

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1793  ax-4 1807  ax-5 1909  ax-6 1967  ax-7 2007

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1778  df-sb 2065

This theorem is referenced by:  sbequi  2084  sbcom3vv  2097  sbco2vv  2099  sbco4lem  2101  sbco4  2102  sbcom2  2174  drsb2  2267  sbco2v  2336  sbcom3  2514  sbco2  2519  sb10f  2535  sb8eulem  2601  eleq1ab  2719  cbvralsvwOLDOLD  3326  cbvrexsvwOLD  3327  cbvralf  3368  cbvralsv  3374  cbvrexsv  3375  cbvreuwOLD  3423  cbvreu  3435  cbvrabwOLD  3482  cbvrab  3487  cbvreucsf  3968  cbvrabcsf  3969  cbvopab1g  5242  cbvmptf  5275  cbvmptfg  5276  cbviota  6535  sb8iota  6537  cbvriota  7418  tfis  7892  tfinds  7897  findes  7940  uzind4s  12973  wl-sbcom2d-lem1  37513  wl-sb8eut  37532  wl-sb8eutv  37533  wl-dfclab  37550  sbeqi  38119  disjinfi  45099  2reu8i  47028