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Mirrors > Home > MPE Home > Th. List > df-fun | Structured version Visualization version GIF version |
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 16102). This is not the same as defining a specific function's mapping, which is typically done using the format of cmpt 5230 with the maps-to notation (see df-mpt 5231 and df-mpo 7435). Contrast this predicate with the predicates to determine if some class is a function with a given domain (df-fn 6565), a function with a given domain and codomain (df-f 6566), a one-to-one function (df-f1 6567), an onto function (df-fo 6568), or a one-to-one onto function (df-f1o 6569). For alternate definitions, see dffun2 6572, dffun3 6576, dffun4 6578, dffun5 6579, dffun6 6575, dffun7 6594, dffun8 6595, and dffun9 6596. (Contributed by NM, 1-Aug-1994.) |
Ref | Expression |
---|---|
df-fun | ⊢ (Fun 𝐴 ↔ (Rel 𝐴 ∧ (𝐴 ∘ ◡𝐴) ⊆ I )) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | cA | . . 3 class 𝐴 | |
2 | 1 | wfun 6556 | . 2 wff Fun 𝐴 |
3 | 1 | wrel 5693 | . . 3 wff Rel 𝐴 |
4 | 1 | ccnv 5687 | . . . . 5 class ◡𝐴 |
5 | 1, 4 | ccom 5692 | . . . 4 class (𝐴 ∘ ◡𝐴) |
6 | cid 5581 | . . . 4 class I | |
7 | 5, 6 | wss 3962 | . . 3 wff (𝐴 ∘ ◡𝐴) ⊆ I |
8 | 3, 7 | wa 395 | . 2 wff (Rel 𝐴 ∧ (𝐴 ∘ ◡𝐴) ⊆ I ) |
9 | 2, 8 | wb 206 | 1 wff (Fun 𝐴 ↔ (Rel 𝐴 ∧ (𝐴 ∘ ◡𝐴) ⊆ I )) |
Colors of variables: wff setvar class |
This definition is referenced by: dffun2 6572 dffun2OLD 6573 dffun2OLDOLD 6574 funrel 6584 funss 6586 nffun 6590 funi 6599 funcocnv2 6873 dffv2 7003 funALTVfun 38679 |
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