Interlinguistics of interlinguistics are, however, not so constructive, but rather descriptive, comparative, historic, sociolinguistic, or concerned with translation by humans or machines. As for Esperanto, which is the most widely used constructed interlanguage, there is a relatively abundant literature about the language itself and its philology (see Esperantology). Only a few of the many constructed languages have been applied practically to any noteworthy extent. The most prosperous were Volapük (1879, Johann Martin Schleyer), Esperanto (1887 Ludwik Lejzer Zamenhof), Latino sine flexione (1903, Giuseppe Peano), Ido (1907, Louis Couturat), Occidental-Interlingue (1922, Edgar de Wahl) and Interlingua (1951, IALA and Alexander Gode), with
Ludwik Kalkstein October 1994, in Munich, Germany. Ludwik Kalkstein Ludwik "Hanka" Kalkstein, also known as Ludwik Kalkstein-Stoliński, (13 March 1920, Warsaw – 26 October 1994, Munich); was one of the better known German Gestapo agents during the Warsaw Uprising as well as a Stalinist informant following the Soviet takeover of Poland. Along with his wife (Blanka Kaczorowska "Sroka"), they became traitors to the Armia Krajowa under not just one but two consecutive totalitarian regimes. Kalkstein was responsible for the arrest and execution by the Nazis of at least fourteen Polish underground officers, including the General Stefan Rowecki. Arrested by the Gestapo in