Two-dimensional (2D) shapes are completely flat. 2D shapes can be found printed in a book or on a website. 2D shapes have sides and corners. A rectangle has 4 straight sides and 4 corners.

asking what four-dimensional shapes can be obtained by deforming four-dimensional Euclidean geometry. In 1981, the Russian-French mathematician Misha Gromov, winner of the Abel Prize, asked whether ...

using carefully conceived geometric shapes to create an optical illusion of depth, and patterns she describes as “moving in a four-dimensional way.” “I realized that in designing ...