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Description: The Null Set Axiom of ZF
set theory: there exists a set with no
elements. Axiom of Empty Set of [Enderton] p. 18. In some textbooks,
this is presented as a separate axiom; here we show it can be derived
from Separation ax-sep 3896. This version of the Null Set Axiom tells us
that at least one empty set exists, but does not tell us that it is
unique - we need the Axiom of Extensionality to do that (see
zfnuleu 3902).
This theorem should not be referenced by any proof. Instead, use ax-nul 3904 below so that the uses of the Null Set Axiom can be more easily identified. (Contributed by Jeff Hoffman, 3-Feb-2008.) (Revised by NM, 4-Feb-2008.) (New usage is discouraged.) (Proof modification is discouraged.) |
Ref | Expression |
---|---|
axnul |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ax-sep 3896 | . 2 | |
2 | pm3.24 659 | . . . . . 6 | |
3 | 2 | intnan 871 | . . . . 5 |
4 | id 19 | . . . . 5 | |
5 | 3, 4 | mtbiri 632 | . . . 4 |
6 | 5 | alimi 1384 | . . 3 |
7 | 6 | eximi 1531 | . 2 |
8 | 1, 7 | ax-mp 7 | 1 |
Colors of variables: wff set class |
Syntax hints: wn 3 wa 102 wb 103 wal 1282 wex 1421 wcel 1433 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 104 ax-ia2 105 ax-ia3 106 ax-in1 576 ax-in2 577 ax-5 1376 ax-gen 1378 ax-ie1 1422 ax-ie2 1423 ax-4 1440 ax-ial 1467 ax-sep 3896 |
This theorem depends on definitions: df-bi 115 |
This theorem is referenced by: (None) |
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