Template:Are You Sure/April 7

• ... that April 7 is National Abuse of Notation Day in the United States; and that while Canada does not have an official Abuse of Notation Day, the phrase "Every Day is Abuse of Notation Day" is often attributed to the mathematician-comedians of New Minneapolis, Canada ?

• ... that computer scientist Donald Sarason pioneered the abstract treatment of contractive containment and established a fruitful connection between the spaces Hb and the ranges of certain Toeplitz operators?

• ... that physicist Ernst Ruhmer (15 April 1878 — 8 April 1913) investigated practical applications making use of the light-sensitivity properties of selenium, which he employed in developing wireless telephony using line-of-sight optical transmission, sound-on-film audio recording, and television transmission over wires?

• ... that physicist and academic Petrus Leonardus Rijke (11 July 1812 – 7 April 1899) explored the physics of electricity, and is known for the Rijke tube, which turns heat into sound by creating a self-amplifying standing wave?