  Mumford proved that psi^g - lambda_1 psi^{g-1} + ... + (-1)^g lambda_g = 0 in
the Chow ring of M_{g,1} [Mum83]. We find an explicit recursive formula for
psi^g - lambda_1 psi^{g-1} + ... + (-1)^g lambda_g in the tautological ring of
\Mbar_{g,1} as a combination of classes supported on boundary strata.
