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Mirrors > Home > MPE Home > Th. List > df-fo | Structured version Visualization version GIF version |
Description: Define an onto function.
Definition 6.15(4) of [TakeutiZaring] p.
27.
We use their notation ("onto" under the arrow). For alternate
definitions, see dffo2 6810, dffo3 7104, dffo4 7105, and dffo5 7106.
An onto function is also called a "surjection" or a "surjective function", 𝐹:𝐴–onto→𝐵 can be read as "𝐹 is a surjection from 𝐴 onto 𝐵". Surjections are precisely the epimorphisms in the category SetCat of sets and set functions, see setcepi 18038. (Contributed by NM, 1-Aug-1994.) |
Ref | Expression |
---|---|
df-fo | ⊢ (𝐹:𝐴–onto→𝐵 ↔ (𝐹 Fn 𝐴 ∧ ran 𝐹 = 𝐵)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | cA | . . 3 class 𝐴 | |
2 | cB | . . 3 class 𝐵 | |
3 | cF | . . 3 class 𝐹 | |
4 | 1, 2, 3 | wfo 6542 | . 2 wff 𝐹:𝐴–onto→𝐵 |
5 | 3, 1 | wfn 6539 | . . 3 wff 𝐹 Fn 𝐴 |
6 | 3 | crn 5678 | . . . 4 class ran 𝐹 |
7 | 6, 2 | wceq 1542 | . . 3 wff ran 𝐹 = 𝐵 |
8 | 5, 7 | wa 397 | . 2 wff (𝐹 Fn 𝐴 ∧ ran 𝐹 = 𝐵) |
9 | 4, 8 | wb 205 | 1 wff (𝐹:𝐴–onto→𝐵 ↔ (𝐹 Fn 𝐴 ∧ ran 𝐹 = 𝐵)) |
Colors of variables: wff setvar class |
This definition is referenced by: foeq1 6802 foeq2 6803 foeq3 6804 nffo 6805 fof 6806 forn 6809 dffo2 6810 dffn4 6812 fores 6816 dff1o2 6839 dff1o3 6840 foimacnv 6851 foun 6852 rescnvimafod 7076 fconst5 7207 dff1o6 7273 nvof1o 7278 f1oweALT 7959 fo1st 7995 fo2nd 7996 tposfo2 8234 fodomr 9128 f1finf1o 9271 f1finf1oOLD 9272 unfilem2 9311 brwdom2 9568 harwdom 9586 infpwfien 10057 alephiso 10093 brdom3 10523 brdom5 10524 brdom4 10525 iunfo 10534 qnnen 16156 isfull2 17862 smndex2dnrinv 18796 odf1o2 19441 cygctb 19760 qtopss 23219 qtopomap 23222 qtopcmap 23223 reeff1o 25959 efifo 26056 bdayfo 27180 pjfoi 30956 fobigcup 34872 tfsconcatfo 42093 fundcmpsurinjlem2 46067 fargshiftfo 46110 |
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