Theorem dfss 3090

Description: Variant of subclass definition df-ss 3089. (Contributed by NM, 3-Sep-2004.)

Assertion

Ref	Expression
dfss	⊢ (𝐴 ⊆ 𝐵 ↔ 𝐴 = (𝐴 ∩ 𝐵))

Proof of Theorem dfss

Step	Hyp	Ref	Expression
1		df-ss 3089	. 2 ⊢ (𝐴 ⊆ 𝐵 ↔ (𝐴 ∩ 𝐵) = 𝐴)
2		eqcom 2142	. 2 ⊢ ((𝐴 ∩ 𝐵) = 𝐴 ↔ 𝐴 = (𝐴 ∩ 𝐵))
3	1, 2	bitri 183	1 ⊢ (𝐴 ⊆ 𝐵 ↔ 𝐴 = (𝐴 ∩ 𝐵))

Syntax hints:   ↔ wb 104   = wceq 1332   ∩ cin 3075   ⊆ wss 3076

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-5 1424  ax-gen 1426  ax-ext 2122

This theorem depends on definitions:  df-bi 116  df-cleq 2133  df-ss 3089

This theorem is referenced by:  dfss2  3091  onelini  4360  cnvcnv  4999  funimass1  5208  sbthlemi5  6857  dmaddpi  7157  dmmulpi  7158  tgioo  12754