Jørgen Mohr (Latinised Georg(ius) Mohr) (1 April 1640 – 26 January 1697) was a Danish mathematician, known for being the first to prove the Mohr–Mascheroni theorem, which states that any geometric construction which can be done with compass and straightedge can also be done with compasses alone.Mohr was born in Copenhagen, the son of a tradesman named David Mohrendal. Beginning in 1662 he traveled to the Netherlands, to study mathematics with Christiaan Huygens.