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Definition df-fun 4934
Description: Define predicate that determines if some class 𝐴 is a function. Definition 10.1 of [Quine] p. 65. For example, the expression Fun I is true (funi 4962). This is not the same as defining a specific function's mapping, which is typically done using the format of cmpt 3847 with the maps-to notation (see df-mpt 3849). Contrast this predicate with the predicates to determine if some class is a function with a given domain (df-fn 4935), a function with a given domain and codomain (df-f 4936), a one-to-one function (df-f1 4937), an onto function (df-fo 4938), or a one-to-one onto function (df-f1o 4939). For alternate definitions, see dffun2 4942, dffun4 4943, dffun6 4946, dffun7 4958, dffun8 4959, and dffun9 4960. (Contributed by NM, 1-Aug-1994.)
Assertion
Ref Expression
df-fun (Fun 𝐴 ↔ (Rel 𝐴 ∧ (𝐴𝐴) ⊆ I ))

Detailed syntax breakdown of Definition df-fun
StepHypRef Expression
1 cA . . 3 class 𝐴
21wfun 4926 . 2 wff Fun 𝐴
31wrel 4376 . . 3 wff Rel 𝐴
41ccnv 4370 . . . . 5 class 𝐴
51, 4ccom 4375 . . . 4 class (𝐴𝐴)
6 cid 4051 . . . 4 class I
75, 6wss 2974 . . 3 wff (𝐴𝐴) ⊆ I
83, 7wa 102 . 2 wff (Rel 𝐴 ∧ (𝐴𝐴) ⊆ I )
92, 8wb 103 1 wff (Fun 𝐴 ↔ (Rel 𝐴 ∧ (𝐴𝐴) ⊆ I ))
Colors of variables: wff set class
This definition is referenced by:  dffun2  4942  funrel  4949  funss  4950  nffun  4954  funi  4962  funcocnv2  5182
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