MATH MAY BE DIFFERENT?  Remo Mannarino  (Rio de Janeiro, February 27, 2020)   Introduction In this book I will present three understandings that go against common sense: (1) Numbers are neutral. There are no positive numbers, no negative numbers. Numerical expressions, not the numbers considered alone, enter in the calculations, doing so under the rules of arithmetic, algebra, geometry, or science. (2) One must learn to multiply. The order of the factors changes the product and it's not true that “less for less gives more”. I can multiply one measurement by another measurement, but I cannot multiply a count by another count. (3) Equations are horizontal tournaments involving "x", but without "y". True equations are of the first degree and have a single unknown. The strange equation of the second degree is an exception, for it has, in two different contexts, a false version with two roots, and a true but playful version with two unkn...