Mathematician:Christopher Clavius

German jesuit and logician.

Best known for:
 * Clavius's Law (also written as Clavius' Law), otherwise known as the Consequentia Mirabilis, which states that if by assuming the negation of a proposition you can prove its truth, then that proposition is true.
 * Being instrumental in the development of the Gregorian calendar.
 * Writing highly-acclaimed and well-received text-books.

Nationality
German

History

 * Born: 25 March 1538, Bamberg (now in Germany)
 * Died: 2 Feb 1612, Rome (now in Italy)

Theorems

 * Clavius's Law

Books and Papers

 * 1574: Published a version of Euclid's, which included some original material of his own, including Clavius's Law.
 * 1593: In sphaeram Ioannis de Sacro Bosco Commentarius
 * 1595: Novi calendarii romani apologia (an argument in favour of the Gregorian calendar, which had been the cause of civil unrest)
 * 1608: Algebra


 * Christophori Clavii e Scoietate Jesu opera mathematica, quinque tomis distributa, a five-volume edition of his collected works, containing the above works and others. Also of note:
 * An edition of Spheric by Theodosius.
 * A commentary on the Tractatus de Sphaera by John of Holywood.