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Definition df-doma 16443
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 doma = (1st ∘ 1st )

Detailed syntax breakdown of Definition df-doma
StepHypRef Expression
1 cdoma 16439 . 2 class doma
2 c1st 7034 . . 3 class 1st
32, 2ccom 5032 . 2 class (1st ∘ 1st )
41, 3wceq 1474 1 wff doma = (1st ∘ 1st )
Colors of variables: wff setvar class
This definition is referenced by:  homadm  16459  dmaf  16468
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