Abraham Lincoln ( February 12, 1809 – April 15, 1865 ) was the 16th President of the United States, serving from March 1861 until his assassination in April 1865.

93, pp. 2686 – 2689, April 1996.

Allan Dwan ( April 3, 1885 – December 28, 1981 ) was a pioneering Canadian-born American motion picture director, producer and screenwriter.

Albert Sidney Johnston ( February 2, 1803 – April 6, 1862 ) served as a general in three different armies: the Texas Army, the United States Army, and the Confederate States Army.

Medical Hypotheses, April 1999 ; 53 ( 4 ): 338 – 344.

Alfred Elton van Vogt ( April 26, 1912 – January 26, 2000 ) was a Canadian-born science fiction author regarded as one of the most popular and complex science fiction writers of the mid-twentieth century: the " Golden Age " of the genre.

* April Fools ' Day – April 1

* Good Friday ( Christians ) – a Friday between March 20 and April 23, being the last Friday before Easter

* Arbor Day ( Korea ) – April 5

* End of Tax Year ( UK ) – April 5

* World Health Day – April 7

* Buddha's Birthday – Traditional Date – April 8

* Araw ng Kagitingan, also known as " Bataan Day " ( Philippines ) – April 9

* Thai New Year in Thailand – April 13

* Lao New Year in Laos – April 13

* Khmer New Year in Cambodia – April 13

* Tax Day ( US ) – April 15

* 4: 20 – April 20

* Patriots ' Day – April 21

* Earth Day – April 22

* Conch Republic Independence Celebration ( Key West, Florida ) – April 23

* St George's Day Patron Saint Celebration ( England, Europe ) – April 23

Eno used SSEYO's Koan generative music system ( created by Pete Cole and Tim Cole of Intermorphic ), to create his hybrid album Generative Music 1 ( published by SSEYO and Opal Arts in April 1996 ), which is probably his first public use of the term " Generative Music ".

An April 2009 issue of the Sage journal Theory & Psychology ( edited by Desmond Painter, Athanasios Marvakis, and Leendert Mos ) is devoted to an examination of German critical psychology.

* Mark A. Satterthwaite, " Strategy-proofness and Arrow's Conditions: Existence and Correspondence Theorems for Voting Procedures and Social Welfare Functions ", Journal of Economic Theory 10 ( April 1975 ), 187 – 217.

After some 25 years of work, his Theory of the Earth ; or an Investigation of the Laws observable in the Composition, Dissolution, and Restoration of Land upon the Globe was read to meetings of the Royal Society of Edinburgh in two parts, the first by his friend Joseph Black on 7 March 1785, and the second by himself on 4 April 1785.

Though Hutton circulated privately a printed version of the abstract of his Theory ( Concerning the System of the Earth, its Duration, and Stability ) which he read at a meeting of the Royal Society of Edinburgh on 4 July 1785 ; the full account of his theory as read at the 7 March 1785 and 4 April 1785 meetings did not appear in print until 1788.

* Calvin, William " Neural Darwinism: The Theory of Neuronal Group Selection ", Science, 24 June 1988, accessed April 16, 2007 ( a review of Gerald Edelman's book Neural Darwinism )

Spurred by the need for enough financial security to marry, Bush finished his thesis, entitled Oscillating-Current Circuits: An Extension of the Theory of Generalized Angular Velocities, with Applications to the Coupled Circuit and the Artificial Transmission Line, in April 1916.

* April 15 – Max Wertheimer, father of Gestalt Theory ( d. 1943 )

Albert Einstein ( 14 March 1879 – 18 April 1955 ) explained the anomalous precession of Mercury's perihelion in his 1916 paper The Foundation of the General Theory of Relativity.

Performers have included Collective Soul, Trooper, Tom Cochrane, April Wine, Sass Jordan, Glass Tiger, Dennis DeYoung, Chantal Kreviazuk, Theory of a Deadman, Kim Mitchell & Max Webster guitarist, Peter Fredette, Finger Eleven, Amanda Marshall and Our Lady Peace.

* John Searle, Expression and Meaning: Studies in the Theory of Speech Acts ( London Review of Books, 17 April 1980 )

* Mills, J. A., " Thomas Brown ’ s Theory of Causation ", Journal of the History of Philosophy, Vol. 22, No. 2, ( April 1984 ), pp. 207 – 227.

* Mark A. Satterthwaite, " Strategy-proofness and Arrow's Conditions: Existence and Correspondence Theorems for Voting Procedures and Social Welfare Functions ", Journal of Economic Theory 10 ( April 1975 ), 187 – 217.

In April 2011 he appeared on The Big Bang Theory in the episode " The Herb Garden Germination " as himself, speaking to a small crowd about the contents of his most recent book.

Theory of Formal Systems: Annals of Mathematics Studies, Princeton University Press ( April 1, 1961 ) 156 pages ISBN 0-691-08047-X

* Straddling Theory with Practice – Conversation with Sir Ralf Dahrendorf by Harry Kreisler of the Institute of International Studies ; 4 April 1989

" A Quantum Theory of Mitt Romney ," his humorous essay written for The New York Times, appeared in April 2012.

The next night at Fighting Spirit on 14 April, Doug made it two for two by defeating Colt Cabana with his Chaos Theory finisher.

* Hans-Georg Beyer: The Theory of Evolution Strategies: Springer April 27, 2001.

Walter Christaller ( April 21, 1893 – March 9, 1969 ), was a German geographer whose principal contribution to the discipline is Central Place Theory, first published in 1933.

* Interview with Alexander Wendt by Theory Talks ( April 2008 )

* Triplett, Jack E. “ Economic Theory and BEA's Alternative Quantity and Price indices ”, Survey of Current Business April 1992.

The majority of the CC responded by producing a document titled " In Support of Differentiation of Three Worlds Theory " in April the same year.

On April 1, 2008, Theory of a Deadman released their third album, Scars & Souvenirs, from which they released eight singles, " So Happy ", " By the Way ", " Little Smirk ", " Bad Girlfriend ", " All or Nothing ", " Hate My Life ", " Not Meant to Be " and " Wait for Me ".

Viterbi decoding was developed by Andrew J. Viterbi and published in the paper " Error Bounds for Convolutional Codes and an Asymptotically Optimum Decoding Algorithm ", IEEE Transactions on Information Theory, Volume IT-13, pages 260-269, in April, 1967.