involution of lines of pencil
1Lie sphere geometry — is a geometrical theory of planar or spatial geometry in which the fundamental concept is the circle or sphere. It was introduced by Sophus Lie in the nineteenth century. [The definitive modern textbook on Lie sphere geometry is Harvnb|Cecil|1992 …
2Lev Vygotsky — Lev Semenovich Vygotsky (Russian: Лев Семёнович Выготский) (November 17 (November 5 Old Style), 1896 – June 11, 1934) was a Russian developmental psychologist and the founder of cultural historical psychology.BiographyVygotsky was born in 1896 in …
