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Mirrors > Home > NFE Home > Th. List > dfpss4 | Unicode version |
Description: Alternate definition of proper subset. Theorem IX.4.21 of [Rosser] p. 236. (Contributed by SF, 19-Jan-2015.) |
Ref | Expression |
---|---|
dfpss4 |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | dfpss3 3355 | . 2 | |
2 | dfss3 3263 | . . . . 5 | |
3 | dfral2 2626 | . . . . 5 | |
4 | 2, 3 | bitr2i 241 | . . . 4 |
5 | 4 | con1bii 321 | . . 3 |
6 | 5 | anbi2i 675 | . 2 |
7 | 1, 6 | bitri 240 | 1 |
Colors of variables: wff setvar class |
Syntax hints: wn 3 wb 176 wa 358 wcel 1710 wral 2614 wrex 2615 wss 3257 wpss 3258 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1546 ax-5 1557 ax-17 1616 ax-9 1654 ax-8 1675 ax-6 1729 ax-7 1734 ax-11 1746 ax-12 1925 ax-ext 2334 |
This theorem depends on definitions: df-bi 177 df-or 359 df-an 360 df-nan 1288 df-tru 1319 df-ex 1542 df-nf 1545 df-sb 1649 df-clab 2340 df-cleq 2346 df-clel 2349 df-nfc 2478 df-ne 2518 df-ral 2619 df-rex 2620 df-v 2861 df-nin 3211 df-compl 3212 df-in 3213 df-ss 3259 df-pss 3261 |
This theorem is referenced by: ssfin 4470 |
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