Editing Almost disjoint sets (section)

==Other meanings==
Sometimes "almost disjoint" is used in some other sense, or in the sense of [[measure (mathematics)|measure theory]] or [[Baire space|topological category]]. Here are some alternative definitions of "almost disjoint" that are sometimes used (similar definitions apply to infinite collections):

*Let κ be any cardinal number. Then two sets ''A'' and ''B'' are almost disjoint if the cardinality of their intersection is less than κ, i.e. if
::<math>\left|A\cap B\right| < \kappa.</math>
:The case of &kappa; = 1 is simply the definition of [[disjoint sets]]; the case of
::<math>\kappa = \aleph_0</math>
:is simply the definition of almost disjoint given above, where the intersection of ''A'' and ''B'' is finite.

*Let ''m'' be a [[measure theory|complete measure]] on a [[measure space]] ''X''. Then two subsets ''A'' and ''B'' of ''X'' are almost disjoint if their intersection is a null-set, i.e. if
::<math>m(A\cap B) = 0.</math>

*Let ''X'' be a [[topological space]]. Then two subsets ''A'' and ''B'' of ''X'' are almost disjoint if their intersection is [[Baire space|meagre]] in ''X''.