Theorem sstr2 3231

Description: Transitivity of subclasses. Exercise 5 of [TakeutiZaring] p. 17. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 14-Jun-2011.)

Assertion

Ref	Expression
sstr2	|- ( A C_ B -> ( B C_ C -> A C_ C ) )

Proof of Theorem sstr2

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		ssel 3218	. . . 4 |- ( A C_ B -> ( x e. A -> x e. B ) )
2	1	imim1d 75	. . 3 |- ( A C_ B -> ( ( x e. B -> x e. C ) -> ( x e. A -> x e. C ) ) )
3	2	alimdv 1925	. 2 |- ( A C_ B -> ( A. x ( x e. B -> x e. C ) -> A. x ( x e. A -> x e. C ) ) )
4		ssalel 3212	. 2 |- ( B C_ C <-> A. x ( x e. B -> x e. C ) )
5		ssalel 3212	. 2 |- ( A C_ C <-> A. x ( x e. A -> x e. C ) )
6	3, 4, 5	3imtr4g 205	1 |- ( A C_ B -> ( B C_ C -> A C_ C ) )

Syntax hints:   -> wi 4   A.wal 1393   e. wcel 2200   C_ wss 3197

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 1493  ax-7 1494  ax-gen 1495  ax-ie1 1539  ax-ie2 1540  ax-8 1550  ax-11 1552  ax-4 1556  ax-17 1572  ax-i9 1576  ax-ial 1580  ax-i5r 1581  ax-ext 2211

This theorem depends on definitions:  df-bi 117  df-nf 1507  df-sb 1809  df-clab 2216  df-cleq 2222  df-clel 2225  df-in 3203  df-ss 3210

This theorem is referenced by:  sstr  3232  sstri  3233  sseq1  3247  sseq2  3248  ssun3  3369  ssun4  3370  ssinss1  3433  ssdisj  3548  triun  4194  trintssm  4197  sspwb  4301  exss  4312  relss  4805  funss  5336  funimass2  5398  fss  5484  fiintim  7089  sbthlem2  7121  sbthlemi3  7122  sbthlemi6  7125  lsslss  14339  lspss  14357  tgss  14731  tgcl  14732  tgss3  14746  clsss  14786  neiss  14818  ssnei2  14825  cnpnei  14887  cnptopco  14890  cnptoprest  14907  txcnp  14939  neibl  15159  metcnp3  15179  bj-nntrans  16272