“By the way, I read in a recent American bookt hat geometry is the art of making no mistakes in long calculations. I think that this is an un-derestimation of geometry.Our brain has two halves: one is responsible for the multiplication of polynomials and languages, and the other half is responsible for orientation of figures in space and all the things important in real life. Mathematics is geometry when you have to use both halves. See, for instance, “The geometry of formulae”