Theorem ssnpss 3373

Description: Partial trichotomy law for subclasses. (Contributed by NM, 16-May-1996.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)

Assertion

Ref	Expression
ssnpss	⊢ (A ⊆ B → ¬ B ⊊ A)

Proof of Theorem ssnpss

Step	Hyp	Ref	Expression
1		dfpss3 3356	. . 3 ⊢ (B ⊊ A ↔ (B ⊆ A ∧ ¬ A ⊆ B))
2	1	simprbi 450	. 2 ⊢ (B ⊊ A → ¬ A ⊆ B)
3	2	con2i 112	1 ⊢ (A ⊆ B → ¬ B ⊊ A)

Syntax hints:  ¬ wn 3   → wi 4   ⊆ wss 3258   ⊊ wpss 3259

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-ne 2519  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-ss 3260  df-pss 3262

This theorem is referenced by: (None)