Blanche Descartes was a collaborative pseudonym used by the English mathematicians R. Leonard Brooks, Arthur Harold Stone, Cedric Smith, and W. T. Tutte.
The pseudonym originated by combining the initials of the mathematicians' given names (Bill, Leonard, Arthur, and Cedric) to form BLAC.
They also discovered "Blanche's Dissection", a method of dividing a square into rectangles of equal area but different dimensions.
[4] Tutte, who is believed to have contributed the most work under Descartes's name, kept up the pretence for years, refusing to acknowledge even in private that she was fictitious.
[6] She also published the poem "Hymne to Hymen"[7] as a gift to Hector Pétard (another fictitious mathematical personage) on the day of his wedding to Betti Bourbaki (daughter of Nicolas Bourbaki, yet another fictitious mathematical personage).