  We have studied the possibility of extracting the $W^+W^-\to W^+W^-$ signal
using the process $us\to cd W^+W^-$ as a test case. We have investigated
numerically the strong gauge cancellations between signal and irreducible
background, analysing critically the reliability of the Equivalent Vector Boson
Approximation which is commonly used to define the signal. Complete matrix
elements are necessary to study Electro--Weak Symmetry Breaking effects at high
$WW$ invariant mass.

High Energy Physics - Phenomenology