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Mirrors > Home > ILE Home > Th. List > dfsbcq | Unicode version |
Description: This theorem, which is
similar to Theorem 6.7 of [Quine] p. 42 and holds
under both our definition and Quine's, provides us with a weak definition
of the proper substitution of a class for a set. Since our df-sbc 2765 does
not result in the same behavior as Quine's for proper classes, if we
wished to avoid conflict with Quine's definition we could start with this
theorem and dfsbcq2 2767 instead of df-sbc 2765. (dfsbcq2 2767 is needed because
unlike Quine we do not overload the df-sb 1646 syntax.) As a consequence of
these theorems, we can derive sbc8g 2771, which is a weaker version of
df-sbc 2765 that leaves substitution undefined when is a proper class.
However, it is often a nuisance to have to prove the sethood hypothesis of sbc8g 2771, so we will allow direct use of df-sbc 2765. Proper substiution with a proper class is rarely needed, and when it is, we can simply use the expansion of Quine's definition. (Contributed by NM, 14-Apr-1995.) |
Ref | Expression |
---|---|
dfsbcq |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | eleq1 2100 | . 2 | |
2 | df-sbc 2765 | . 2 | |
3 | df-sbc 2765 | . 2 | |
4 | 1, 2, 3 | 3bitr4g 212 | 1 |
Colors of variables: wff set class |
Syntax hints: wi 4 wb 98 wceq 1243 wcel 1393 cab 2026 wsbc 2764 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 99 ax-ia2 100 ax-ia3 101 ax-5 1336 ax-gen 1338 ax-ie1 1382 ax-ie2 1383 ax-4 1400 ax-17 1419 ax-ial 1427 ax-ext 2022 |
This theorem depends on definitions: df-bi 110 df-cleq 2033 df-clel 2036 df-sbc 2765 |
This theorem is referenced by: sbceq1d 2769 sbc8g 2771 spsbc 2775 sbcco 2785 sbcco2 2786 sbcie2g 2796 elrabsf 2801 eqsbc3 2802 csbeq1 2855 sbcnestgf 2897 sbcco3g 2903 cbvralcsf 2908 cbvrexcsf 2909 findes 4326 ralrnmpt 5309 rexrnmpt 5310 findcard2 6346 findcard2s 6347 ac6sfi 6352 nn1suc 7933 uzind4s2 8534 indstr 8536 |
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