df-doma - Metamath Proof Explorer

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Definition df-doma 18042

Description: Definition of the domain extractor for an arrow. (Contributed by FL, 24-Oct-2007.) (Revised by Mario Carneiro, 11-Jan-2017.)

**Assertion**
Ref	Expression
df-doma	⊢ dom_a = (1^st ∘ 1^st )

**Detailed syntax breakdown of Definition df-doma**
Step	Hyp	Ref	Expression
1		cdoma 18038	. 2 class dom_a
2		c1st 7991	. . 3 class 1^st
3	2, 2	ccom 5663	. 2 class (1^st ∘ 1^st )
4	1, 3	wceq 1540	1 wff dom_a = (1^st ∘ 1^st )

Colors of variables: wff setvar class

This definition is referenced by: homadm 18058 dmaf 18067