  If \chi^\lambda is the irreducible character of the symmetric group S_n
corresponding to the partition \lambda of n then we may symmetrize a tensor v_1
\otimes ... \otimes v_n by \chi^\lambda. Gamas's theorem states that the result
is not zero if and only if we can partition the set {v_i} into linearly
independent sets whose sizes are the parts of the transpose of \lambda. We give
a short and self-contained proof of this fact.
