spˈɛʃəl kˈeɪsᵻz hɐvbɪn nˈoʊn sˈɪns æntˈɪkwᵻɾi, ænd ðə dʒˈɛnɚɹəl kˈeɪs wʌz stˈʌdid baɪ dʒˈiːn ɡˈæstən dˈɑːɹbuː.
Special cases have been known since antiquity, and the general case was studied by Jean Gaston Darboux.