The quantum formalism permits one to discriminate sometimes between any set
of linearly independent pure states with certainty. We obtain the maximum
probability with which a set of equally likely, symmetric, linearly indepen
dent states can be discriminated. The form of this bound is examined for sy
mmetric coherent states of a harmonic oscillator or field mode. (C) 1998 Pu
blished by Elsevier Science B.V.