In this work, we establish the relations between neural networks and hierar
chies of quasiarithmetic means. We show that a neural network with the same
activation function in all the neurons gives an output that is isomorphic
to the result that can be obtained with a hierarchy of quasiarithmetic mean
s. From this result, we-show that hierarchies of quasiarithmetic means are
universal approximations. (C) 1999 John Wiley & Sons, Inc.