Theorem ssid

Description: Any class is a subclass of itself. Exercise 10 of TakeutiZaring p. 18. (Contributed by NM, 21-Jun-1993) (Proof shortened by Andrew Salmon, 14-Jun-2011)

	Ref	Expression
Assertion	ssid	⊢ 𝐴 ⊆ 𝐴

Proof

Step	Hyp	Ref	Expression
1		id	⊢ ( 𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐴 )
2	1	ssriv	⊢ 𝐴 ⊆ 𝐴