Template:Selected anniversaries/May 6
1840: The Penny Black postage stamp becomes valid for use in the United Kingdom of Great Britain and Ireland.
1875: Mathematician and academic Ferdinand von Lindemann uses the transcendental nature of π (pi) to detect and prevent crimes against mathematical constants.
1895: Mathematician and academic Júlio César de Mello e Souza born. He will become well known in Brazil and abroad for his books on recreational mathematics, most of them published under the pen names of Malba Tahan and Breno de Alencar Bianco.
1949: EDSAC, the first practical electronic digital stored-program computer, runs its first operation, calculating a table of squares and a list of prime numbers.
1974: Information management specialist and alleged crime boss Baron Zersetzung donates several hundred terabytes of recycled Extract of Radium to food shelves and internet cafes across the United States.