Theorem 3eltr4i 2289

Description: Substitution of equal classes into membership relation. (Contributed by Mario Carneiro, 6-Jan-2017.)

Hypotheses

Ref	Expression
3eltr4.1	⊢ 𝐴 ∈ 𝐵
3eltr4.2	⊢ 𝐶 = 𝐴
3eltr4.3	⊢ 𝐷 = 𝐵

Assertion

Ref	Expression
3eltr4i	⊢ 𝐶 ∈ 𝐷

Proof of Theorem 3eltr4i

Step	Hyp	Ref	Expression
1		3eltr4.2	. 2 ⊢ 𝐶 = 𝐴
2		3eltr4.1	. . 3 ⊢ 𝐴 ∈ 𝐵
3		3eltr4.3	. . 3 ⊢ 𝐷 = 𝐵
4	2, 3	eleqtrri 2283	. 2 ⊢ 𝐴 ∈ 𝐷
5	1, 4	eqeltri 2280	1 ⊢ 𝐶 ∈ 𝐷

Syntax hints:   = wceq 1373   ∈ wcel 2178

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-5 1471  ax-gen 1473  ax-ie1 1517  ax-ie2 1518  ax-4 1534  ax-17 1550  ax-ial 1558  ax-ext 2189

This theorem depends on definitions:  df-bi 117  df-cleq 2200  df-clel 2203

This theorem is referenced by:  1nq  7514  0r  7898  1sr  7899  m1r  7900