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Metamath Proof Explorer

Theorem ordelpss

Description: For ordinal classes, membership is equivalent to strict inclusion. Corollary 7.8 of TakeutiZaring p. 37. (Contributed by NM, 17-Jun-1998)

		Ref	Expression
	Assertion	ordelpss	⊢ ( ( Ord 𝐴 ∧ Ord 𝐵 ) → ( 𝐴 ∈ 𝐵 ↔ 𝐴 ⊊ 𝐵 ) )

Proof

Step	Hyp	Ref	Expression
1		ordelssne	⊢ ( ( Ord 𝐴 ∧ Ord 𝐵 ) → ( 𝐴 ∈ 𝐵 ↔ ( 𝐴 ⊆ 𝐵 ∧ 𝐴 ≠ 𝐵 ) ) )
2		df-pss	⊢ ( 𝐴 ⊊ 𝐵 ↔ ( 𝐴 ⊆ 𝐵 ∧ 𝐴 ≠ 𝐵 ) )
3	1 2	bitr4di	⊢ ( ( Ord 𝐴 ∧ Ord 𝐵 ) → ( 𝐴 ∈ 𝐵 ↔ 𝐴 ⊊ 𝐵 ) )