  We obtain a formula which reduces the evaluation of a $_2\psi_2$ series to
two $_2\phi_1$ series. In some sense, this identity may be considered as a
companion of Slater's formulas. We also find that a two-term ${}_2\psi_2$
summation formula due to Slater can be derived from a unilateral summation
formula of Andrews by bilateral extension and parameter augmentation.
