Several researchers characterized the activation functions under which multilayer feedforward
networks can act as universal approximators. We show that all the characterizations
that were reported thus far in the literature ark special cases of the following general result:
a standard multilayer feedforward network can approximate any continuous function
to any degree of accuracy if and only if the network's activation functions are not polynomial.
We also emphasize the important role of the threshold, asserting that without it the
last theorem doesn't hold.Information Systems Working Papers Serie