We estimate variation with respect to half-spaces in terms of ''flows
through hyperplanes''. Our estimate is derived from an integral repres
entation for smooth compactly supported multivariable functions proved
using properties of the Heaviside and delta distributions. Consequent
ly we obtain conditions which guarantee approximation error rate of or
der O(1/root n) by one-hidden-layer networks with n sigmoidal perceptr
ons. (C) 1997 Elsevier Science Ltd.