Theorem eliminable3a

Description: A theorem used to prove the base case of the Eliminability Theorem (see section comment). (Contributed by BJ, 19-Oct-2019) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	eliminable3a	$$⊢\left\{x|\phi \right\}\in y\leftrightarrow \exists z\left(z=\left\{x|\phi \right\}\wedge z\in y\right)$$

Proof

Step	Hyp	Ref	Expression
1		dfclel	$$⊢\left\{x|\phi \right\}\in y\leftrightarrow \exists z\left(z=\left\{x|\phi \right\}\wedge z\in y\right)$$