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Definition df-fun 5273
Description: Define predicate that determines if some class  A is a function. Definition 10.1 of [Quine] p. 65. For example, the expression  Fun  cos is true once we define cosine (df-cos 12368). This is not the same as defining a specific function's mapping, which is typically done using the format of cmpt 4093 with the maps-to notation (see df-mpt 4095 and df-mpt2 5879). Contrast this predicate with the predicates to determine if some class is a function with a given domain (df-fn 5274), a function with a given domain and codomain (df-f 5275), a one-to-one function (df-f1 5276), an onto function (df-fo 5277), or a one-to-one onto function (df-f1o 5278). For alternate definitions, see dffun2 5281, dffun3 5282, dffun4 5283, dffun5 5284, dffun6 5286, dffun7 5296, dffun8 5297, and dffun9 5298. (Contributed by NM, 1-Aug-1994.)
Assertion
Ref Expression
df-fun  |-  ( Fun 
A  <->  ( Rel  A  /\  ( A  o.  `' A )  C_  _I  ) )

Detailed syntax breakdown of Definition df-fun
StepHypRef Expression
1 cA . . 3  class  A
21wfun 5265 . 2  wff  Fun  A
31wrel 4710 . . 3  wff  Rel  A
41ccnv 4704 . . . . 5  class  `' A
51, 4ccom 4709 . . . 4  class  ( A  o.  `' A )
6 cid 4320 . . . 4  class  _I
75, 6wss 3165 . . 3  wff  ( A  o.  `' A ) 
C_  _I
83, 7wa 358 . 2  wff  ( Rel 
A  /\  ( A  o.  `' A )  C_  _I  )
92, 8wb 176 1  wff  ( Fun 
A  <->  ( Rel  A  /\  ( A  o.  `' A )  C_  _I  ) )
Colors of variables: wff set class
This definition is referenced by:  dffun2  5281  funrel  5288  funss  5289  nffun  5293  funi  5300  funcocnv2  5514  dffv2  5608
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