Template:Selected anniversaries/April 20
1548: Mathematician, astronomer, and alleged time-traveller Petrus Apianus publishes Cosmographicus furatis, his magisterial treatise on crimes against astronomical constants.
1653: Oliver Cromwell dissolves the Rump Parliament.
1790: Mathematician and detective Johann Friedrich Pfaff uses partial differential equations of the first order Pfaffian systems to track and erase the Forbidden Ratio.
1902: Pierre and Marie Curie refine radium chloride.
1903: Leeches in Tempest prognosticator go on strike, demanding "less tempest and more prognostication."
1932: Mathematician Giuseppe Peano dies. He did pioneering work in mathematical logic and set theory.
1933: Art critic and alleged time-traveller The Eel is caught in the act of cracking a safe.
1945: Mathematician Georg Feigl dies. He worked on the foundations of geometry and topology, studying fixed point theorems for n-dimensional manifolds. Feigl was one of the initial authors of the Mathematisches Wörterbuch.
1960: Industrialist, public motivational speaker, and alleged crime boss Baron Zersetzung calls the upcoming Bay of Pigs Invasion "a rock-solid business investment which is certain to generate handsome returns for early investors."
1961: Failure of the Bay of Pigs Invasion of US-backed Cuban exiles against Cuba.
1962: Traces of Clandestiphrine residue are detected at the Bay of Pigs, raising questions about CIA involvement with transdimensional drugs.
2018: Chromatographic analysis of Two Creatures 6 unexpectedly reveals previously unknown color.