Conull set

In measure theory, a conull set is a set whose complement is null, i.e., the measure of the complement is zero.{{citation

| last = Führ | first = Hartmut

| isbn = 3-540-24259-7

| mr = 2130226

| page = 12

| publisher = Springer-Verlag, Berlin

| series = Lecture Notes in Mathematics

| title = Abstract harmonic analysis of continuous wavelet transforms

| url = https://books.google.com/books?id=ERlIzB67I9kC&pg=PA12

| volume = 1863

| year = 2005}}. For example, the set of irrational numbers is a conull subset of the real line with Lebesgue measure.A related but slightly more complex example is given by Führ, p. 143.

A property that is true of the elements of a conull set is said to be true almost everywhere.{{citation

| last = Bezuglyi | first = Sergey

| contribution = Groups of automorphisms of a measure space and weak equivalence of cocycles

| mr = 1774424

| pages = 59–86

| publisher = Cambridge Univ. Press, Cambridge

| series = London Math. Soc. Lecture Note Ser.

| title = Descriptive set theory and dynamical systems (Marseille-Luminy, 1996)

| volume = 277

| year = 2000}}. See [https://books.google.com/books?id=g64TCEiYULAC&pg=PA62 p. 62] for an example of this usage.