What is now known as the Cauchy-Schwarz inequality was rst mentioned in a note by Augustin-Louis Cauchy in 1821, published in connection with his book Course d'Analyse Algébrique. His original inequality was formulated in terms of sequences in R, but later Viktor Yakovlevich Bunyakovsky proved the analog version for integrals in his Mémoire(1859). In the course of his work on minimal surfaces Karl Hermann Amandus Schwarz in 1885 proved the inequality for two- dimensional integrals, apparently not knowing about Bunyakovsky's work. Due to Bunyakovsky's relative obscurity in the West at the time, the inequality came to be known as the Cauchy-Schwarz inequality, as opposed to, for instance, the Cauchy-Bunyakovsky-Schwarz inequality.
In keeping with mathematical tradition over historical precedence we will use the name Cauchy-Schwarz inequality, or CS inequality for short. As we will see, the inequality is valid in considerably more general cases than the ones thus far mentioned. We will not distinguish much between the di erent versions of the inequality, for our purposes they are all the CS inequality.