Nomographic functions are nowhere dense

Abstract : An important topic in approximation theory is the study of ways to approximate complicated functions of many variables by combinations of simpler functions. One important type of the latter are the nomographic functions, which can be written entirely in terms of addition and functions of one variable. The present paper shows that these are inherently a very sparse subset of the class of all continuous functions; this places a severe limitation upon their use as single functions, but not if they are added together.