Template:Are You Sure/April 7

• ... that physicist Ernst Ruhmer (April 15, 1878—April 8, 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 computer scientist Donald Sarason (January 26, 1933 – April 8, 2017) pioneered the abstract treatment of contractive containment and established a fruitful connection between the spaces Hb and the ranges of certain Toeplitz operators?