Julius Wilhelm Richard Dedekind
The life of Julius Wilhelm Richard Dedekind - the "Dedekind Cut"
Dedekind Cuts
A method of constructing the real numbers from the rational numbers.
\[ x = \{ q \in \mathbb{Q} \mid q < r \} \]
Sources: https://mathshistory.st-andrews.ac.uk/Biographies/Dedekind/