Theorem 3sstr4i 3225

Description: Substitution of equality in both sides of a subclass relationship. (Contributed by NM, 13-Jan-1996.) (Proof shortened by Eric Schmidt, 26-Jan-2007.)

Hypotheses

Ref	Expression
3sstr4.1	⊢ 𝐴 ⊆ 𝐵
3sstr4.2	⊢ 𝐶 = 𝐴
3sstr4.3	⊢ 𝐷 = 𝐵

Assertion

Ref	Expression
3sstr4i	⊢ 𝐶 ⊆ 𝐷

Proof of Theorem 3sstr4i

Step	Hyp	Ref	Expression
1		3sstr4.1	. 2 ⊢ 𝐴 ⊆ 𝐵
2		3sstr4.2	. . 3 ⊢ 𝐶 = 𝐴
3		3sstr4.3	. . 3 ⊢ 𝐷 = 𝐵
4	2, 3	sseq12i 3212	. 2 ⊢ (𝐶 ⊆ 𝐷 ↔ 𝐴 ⊆ 𝐵)
5	1, 4	mpbir 146	1 ⊢ 𝐶 ⊆ 𝐷

Syntax hints:   = wceq 1364   ⊆ wss 3157

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 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-11 1520  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-ext 2178

This theorem depends on definitions:  df-bi 117  df-nf 1475  df-sb 1777  df-clab 2183  df-cleq 2189  df-clel 2192  df-in 3163  df-ss 3170

This theorem is referenced by:  undif2ss  3527  pwsnss  3834  iinuniss  4000  brab2a  4717  relopabiv  4790  rncoss  4937  imassrn  5021  rnin  5080  inimass  5087  imadiflem  5338  imainlem  5340  ssoprab2i  6015  npsspw  7555  axresscn  7944  mpomulf  8033