The development leading to Cantor's 1874 article appears in the correspondence between Cantor, and [[Richard Dedekind]]. On November 29, 1873, Cantor asked Dedekind whether the collection of positive integers and the collection of positive real numbers "can be corresponded so that each individual of one collection corresponds to one and only one individual of the other?" Cantor added that collections having such a correspondence include the collection of positive rational numbers, and collections of the form (''a''<sub>''n''<sub>1</sub>, ''n''<sub>2</sub>, . . . , ''n''<sub>''ν''</sub></sub>) where ''n''<sub>1</sub>, ''n''<sub>2</sub>, . . . , ''n''<sub>''ν''</sub>, and ''ν'' are positive integers.<ref>{{harvnb|Noether|Cavaillès|1937|pp=12–13}}. English translation: {{harvnb|Gray|1994|p=827}}; {{harvnb|Ewald|1996|p=844}}.</ref>
Dedekind replied that he was unable to answer Cantor's question, and said that it "did not deserve too much effort because it has no particular practical interest." Dedekind also sent Cantor a proof that the set of algebraic numbers is countable.<ref name=Noether18>{{harvnb|Noether|Cavaillès|1937|p=18}}. English translation: {{harvnb|Ewald|1996|p=848}}.</ref>
