Empty set
Description
The empty set is the set that has no elements. It is written or . For each object , . By the axiom of extensionality, there is only one empty set.
Remarks
The empty set is a subset of every set. This is a case of vacuous truth. Its cardinality is . The set is not empty: it has one element.
Explanations
L1 human
The empty set is an empty bag. For example, the set of real numbers with is empty. It is useful in the same way that the number is useful.
What this node needs for W2
- section Invariants: a table of the main invariants (0 of 1)
The writing levels say how complete the text of a node is. They do not measure its truth.
What depends on this
149 nodes use this node, directly or through other nodes.
- Closure is the set of limits of sequences 003QP7A8HG
- Finite intersection property 00BWV5CKCF
- Prior probability 00NBBSXRQS
- Compact set 00R0X1WGPX
- Second-countable space 00RE1R4W7N
- Chapman–Kolmogorov equation 01APZ8GDQH
- Totally disconnected space 01CYW8S04D
- Urysohn's lemma 01EY3VR7ZD
- Equivalence classes form a partition 01HT2CH8BH
- Isolated point 01PKQYTTMT
- Cantor set is closed 01VT24J1SD
- Open set 01ZQQDCERP
- Open balls form a basis of the metric topology 02EEX96DFS
- Closure is closed 02TZDKG50Q
- Arzelà–Ascoli theorem 0381S8Z5P0
- Law of total variance 03BY5XTNA4
- Equivalence of norms in finite dimension 03MC70ZRNR
- Torus 03NM7DZXXC
- Lebesgue number lemma 040CFNJEAP
- Continuous bijection from a compact space to a Hausdorff space is a homeomorphism 0430ETCMKD
- Möbius strip 04AJE0M271
- Law of total expectation 04RRB6HM00
- Product topology on an arbitrary product 04S9HX3GAP
- Compact iff complete and totally bounded 054Q5PW5GX
- T1 space 05GQJXBP3F
- Homeomorphism 05GZ11PWRY
- Composition of continuous maps is continuous 05NK26G0DR
- Inclusion of a subspace is continuous 065J822CKN
- Closed subsets of compact sets are compact 066HW6D9A7
- Closure in a metric space 068P0P32DW
- Heine–Cantor theorem 06B8BNJCD6
- Basis of a topology 06EX0FHBTF
- Correspondence between equivalence relations and partitions 074482Q7CD
- Continuity at a point of a topological space 07N7W5C29X
- Heine–Borel theorem 07PFYV65MB
- Absolutely convergent series in a Banach space converge 082MGNWNA8
- Sequence spaces lp 08P6T2WH6R
- Topological embedding 08SVRVHJNY
- Comparison of topologies 08XFJJ8EYW
- Riesz's lemma 097C7KCAT5
- Intermediate value theorem for connected spaces 098C0KZZAP
- Partition of a set 09CCE86A6D
- Open sets characterised by neighbourhoods 09CJ00H3NW
- Closed sets contain their limits 09GQ3ZTQJ9
- Completeness of the space of bounded continuous functions 09GRCZVR5E
- Metrizable space 09KDHB82SG
- Finite intersection of open sets is open 09NDE9V7X1
- Intersection of closed sets is closed 09YMV8H4X5
- Product of compact sets is compact 09ZKE5XQ74
- Open sets of a metric space 0A26X79RTB
- Metric topology 0A6YRNZB2R
- Baire category theorem 0A7KGAYHGV
- Finite-dimensional normed spaces are complete 0ABP2F2ZP7
- Metrizable spaces are normal 0AD0BZ49DW
- Normal space 0AJ646N339
- Open balls are open 0B2305GNAZ
- Continuity via closed sets 0B8GPXFSP7
- Connected subsets of the real line are intervals 0B9ZQFMQNV
- Banach space 0BDTTM24DP
- Linear maps on finite-dimensional spaces are continuous 0C13E623WD
- Interior 0C38S0KMJK
- Sequential compactness 0CARW59WD2
- Subbasis 0CHR35YNJQ
- Topological space 0CNQXVBHCX
- Box topology 0CTM1EHG9P
- Dense set 0D198GPMTJ
- A set is closed iff it equals its closure 0D2W7FS52T
- Baire space 0D5KR33H7X
- Subspace topology 0D5YHQGDJY
- Limits are unique in Hausdorff spaces 0D8T984XEE
- Connected space 0D939CMME7
- Closure 0DRKT1QJR7
- Base rate fallacy 0E44JMG6NV
- Law of total probability 0E5G5FMT2R
- Epsilon-delta continuity in metric spaces 0EKGKY5TGH
- Continuous image of a connected set is connected 0EPD87YVG8
- Locally compact space 0EQMWQ4WMJ
- Cantor's intersection theorem 0EZBG8SKJM
- Bounded linear maps are continuous 0F3K4C7XYW
- Closed subsets of complete spaces are complete 0FBXJZX3MK
- Universal property of the quotient topology 0FF2FJ8CH2
- Meagre set 0FQPYAY9PJ
- Completion of a metric space 0G4J7Z7WPJ
- Closed set 0G5AV9Q4RR
- Separable space 0GKJ78948V
- Interior is the largest open subset 0HAZEFH137
- Limit point 0HBQC2GJXT
- Union of open sets is open 0HEF46RPEK
- First-countable space 0HG11FW8MJ
- Equivalent norms 0J3578562S
- Regular space 0JF9KW2TXB
- Boundary 0JJ9J1XZ8G
- Tychonoff's theorem 0JTRSJKCFB
- Bayesian inference 0JWRJX2RMP
- Path-connected space 0K0GE6BCYW
- Topologist's sine curve 0K3T4A659R
- Complement of an open set is closed 0K67Q60Z8P
- Compactness and sequential compactness agree in metric spaces 0K8SGQSV7G
- Continuous image of a compact set is compact 0K9AAJ8G51
- Posterior probability 0KJ7ZS8AJA
- p-norm on R^n 0KNJWEVSMG
- Nowhere dense set 0KSM23SN3H
- Universal property of the product topology 0M6W4XNST6
- One-point compactification 0MM45BT6HC
- Compact Hausdorff spaces are normal 0MQQQ5NA2S
- Equicontinuity 0MW2WXTHMC
- Hausdorff space 0MXB4CKHFW
- Open connected subsets of R^n are path-connected 0MXN7AFBPE
- Compact subsets of a Hausdorff space are closed 0MYFJVMN7M
- Bayes' theorem 0NM6E9VW04
- Connected components are closed 0NRT0E2QT2
- Open cover 0NVPNC12JY
- Closed map 0NYZ2M45G9
- Compactness via open covers 0P6PMJB4MA
- Metric spaces are Hausdorff 0P9DCDES73
- Sup norm on bounded continuous functions 0PARCKE8WP
- Monty Hall problem 0PBWWQD9KY
- Heine–Borel theorem in finite-dimensional normed spaces 0PHT6NBYPB
- Projections are continuous 0PM88Z9W4M
- Interior is open 0PNWCM559P
- Compact space 0QPHW703PV
- Connected set 0R37DFJKFW
- T0 space 0R3B7DX55J
- Compact subsets of a metric space are bounded 0R7BTEWCJ2
- Cantor set is homeomorphic to the space of binary sequences 0RQ8DHHR8V
- Continuous linear map 0S3SMRH0Z5
- Path component 0SB9FNZECG
- Closure is the smallest closed superset 0SHC6Z304Z
- Open map 0SQ2PC596Y
- Continuous map of topological spaces 0SY9ECQ19Q
- Equivalent metrics 0TWQ5PRKWS
- Continuous real function on a compact set attains its bounds 0V4DET59NW
- Quotient topology 0V8046R0P9
- Continuity is equivalent to sequential continuity in metric spaces 0VGPKZ8MRK
- Compact closed unit ball implies finite dimension 0VZVV8VME5
- Complete subspaces are closed 0W41XG4W60
- Disjoint sets 0W4RPA8QH3
- Law of total probability for an event and its complement 0W62TKMW7V
- Gambler's ruin 0WFMKK7DFZ
- Circle as a quotient of the real line 0WH1GVBJNH
- Countable intersection of dense open sets is dense 0X2T63GFQQ
- Tietze extension theorem 0X52TNMTCJ
- Absorbing Markov chain 0YB93GWTKK
- Continuity via open sets 0YF82GBTND
- Closed balls are closed 0YS40B38JD
- Proper metric space 0Z4V98VN5E
- Product topology 0Z57EC6YX3
- Path-connected spaces are connected 0ZMT1GP4KM
- Operator norm 0ZTEH055YF
Sources
- Web https://en.wikipedia.org/wiki/Empty_set, lead section
What links here
Used by
- Topological space 0CNQXVBHCX
- Disjoint sets 0W4RPA8QH3