A misleading example of a test function in space D from textbooks on   Generalized Functions and Distributions
  In many textbooks on Generalized Functions and Distributions, we can find an example of infinitely differentiable function of bounded support from space D, called a bump function. This example is incorrect since this function is not infinitely differentiable. 
A. Tsionskiy, M. Tsionskiy
math-ph math.FA math.MP