Theorem sstrd 3283

Description: Subclass transitivity deduction. (Contributed by NM, 2-Jun-2004.)

Hypotheses

Ref	Expression
sstrd.1	|- (ph -> A C_ B)
sstrd.2	|- (ph -> B C_ C)

Assertion

Ref	Expression
sstrd	|- (ph -> A C_ C)

Proof of Theorem sstrd

Step	Hyp	Ref	Expression
1		sstrd.1	. 2 |- (ph -> A C_ B)
2		sstrd.2	. 2 |- (ph -> B C_ C)
3		sstr 3281	. 2 |- ((A C_ B /\ B C_ C) -> A C_ C)
4	1, 2, 3	syl2anc 642	1 |- (ph -> A C_ C)

Syntax hints:   -> wi 4   C_ wss 3258

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-ss 3260

This theorem is referenced by:  syl5ss  3284  syl6ss  3285  ssdif2d  3406  uniintsn  3964  funss  5127