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Definition df-fun 4683
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 12315). This is not the same as defining a specific function's mapping, which is typically done using the format of cmpt 4051 with the maps-to notation (see df-mpt 4053 and df-mpt2 5797). Contrast this predicate with the predicates to determine if some class is a function with a given domain (df-fn 4684), a function with a given domain and codomain (df-f 4685), a one-to-one function (df-f1 4686), an onto function (df-fo 4687), or a one-to-one onto function (df-f1o 4688). For alternate definitions, see dffun2 5204, dffun3 5205, dffun4 5206, dffun5 5207, dffun6 5209, dffun7 5219, dffun8 5220, and dffun9 5221. (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 4667 . 2  wff  Fun  A
31wrel 4666 . . 3  wff  Rel  A
41ccnv 4660 . . . . 5  class  `' A
51, 4ccom 4665 . . . 4  class  ( A  o.  `' A )
6 cid 4276 . . . 4  class  _I
75, 6wss 3127 . . 3  wff  ( A  o.  `' A ) 
C_  _I
83, 7wa 360 . 2  wff  ( Rel 
A  /\  ( A  o.  `' A )  C_  _I  )
92, 8wb 178 1  wff  ( Fun 
A  <->  ( Rel  A  /\  ( A  o.  `' A )  C_  _I  ) )
Colors of variables: wff set class
This definition is referenced by:  dffun2  5204  funrel  5211  funss  5212  nffun  5216  funi  5223  funcocnv2  5436  dffv2  5526
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