Theorem pssn2lp 4104

Description: Proper subclass has no 2-cycle loops. Compare Theorem 8 of [Suppes] p. 23. (Contributed by NM, 7-Feb-1996.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)

Assertion

Ref	Expression
pssn2lp	⊢ ¬ (𝐴 ⊊ 𝐵 ∧ 𝐵 ⊊ 𝐴)

Proof of Theorem pssn2lp

Step	Hyp	Ref	Expression
1		dfpss3 4089	. . . 4 ⊢ (𝐴 ⊊ 𝐵 ↔ (𝐴 ⊆ 𝐵 ∧ ¬ 𝐵 ⊆ 𝐴))
2	1	simprbi 496	. . 3 ⊢ (𝐴 ⊊ 𝐵 → ¬ 𝐵 ⊆ 𝐴)
3		pssss 4098	. . 3 ⊢ (𝐵 ⊊ 𝐴 → 𝐵 ⊆ 𝐴)
4	2, 3	nsyl 140	. 2 ⊢ (𝐴 ⊊ 𝐵 → ¬ 𝐵 ⊊ 𝐴)
5		imnan 399	. 2 ⊢ ((𝐴 ⊊ 𝐵 → ¬ 𝐵 ⊊ 𝐴) ↔ ¬ (𝐴 ⊊ 𝐵 ∧ 𝐵 ⊊ 𝐴))
6	4, 5	mpbi 230	1 ⊢ ¬ (𝐴 ⊊ 𝐵 ∧ 𝐵 ⊊ 𝐴)

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 395   ⊆ wss 3951   ⊊ wpss 3952

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2007  ax-9 2118  ax-ext 2708

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1780  df-cleq 2729  df-ne 2941  df-ss 3968  df-pss 3971

This theorem is referenced by:  psstr  4107  cvnsym  32309