  Forces beyond those of the standard model may manifest themselves at low
energies as four-fermion contact interactions. If these new forces are
independent of colour and flavour quantum numbers including baryon and lepton
number, then all low energy constraints, arising from quark-lepton
universality, flavour-changing neutral currents and atomic parity violation are
evaded. This is due to the global U(45) symmetry which the standard model
exhibits in the limit of vanishing gauge and Yukawa couplings. The
corresponding contact interaction is a unique current-current interaction.
Constraints from LEP2 imply that this universal contact interaction cannot be
the origin of the recently observed high-$Q^2$ events at HERA.
