Assertion: triangle | /r/HasProperty | popularized in 1950
Facets:
value: by his son
type: OTHER
value: by psychiatrist lionel penrose
type: OTHER
Source sentences:
text: Independently from Reutersvärd, the triangle was devised and popularized in the 1950s by psychiatrist Lionel Penrose and his son, prominent mathematician Roger Penrose, who described it as "impossibility in its purest form".