1 Cubism was invented around 1907 in Paris by Pablo Picasso and Georges Braque. 2  Cubism was the first abstract style of modern art. 3  A Cubist painting ignores the traditions of perspective drawing and shows you many views of a subject at one time. 4  The Cubists introduced collage into painting.
Two linear systems using the same set of variables are equivalent if each of the equations in the second system can be derived algebraically from the equations in the first system, and vice versa.
An equivalent definition is that every sequence of points must have an infinite subsequence that converges to some point of the space. The Heine-Borel theorem states that a subset of Euclidean space is compact in this sequential sense if and only if it is closed and bounded.