Example image of eyePlorer eyePlorer map for 'Empty set': 0 (number) Element (mathematics) Mathematics Set (mathematics) Set theory Axiom of empty set Trivial (mathematics) Measure (mathematics) Null set André Weil Danish and Norwegian alphabet Nicolas Bourbaki Ø Axiom of extensionality Table of mathematical symbols Cardinality Cartesian product Intersection (set theory) Power set Subset Union (set theory) Finite set Model theory Set-theoretic definition of natural numbers Vacuous truth 1 (number) Empty product Multiplication Summation Identity element Ordered set Real line Extended real number line Infimum Supremum Clopen set Closed set Open set Topological space Boundary (topology) Neighbourhood (mathematics) Compact space Closure (mathematics) Arity Empty function Function (mathematics) Category theory Initial and terminal objects Category of topological spaces Continuous function (topology)