  Most of this paper consists of the derivation of general beam-referenced
stage-two spin-correlation functions for the analysis of top-antitop
pair-production at the Tevatron, at the Large Hadron Collider, and/or at an
International Linear Collider. However, for the charged-lepton-plus-jets
reaction $q \bar{q} \to t \bar{t} \to (W^+ b) (W^- \bar{b}) \to (l^{+} \nu b)
(W^- \bar{b})$, there is a simple 3-angle spin-correlation function for
determination of the relative sign of, or for measurement of a possible
non-trivial phase between the two dominant $\lambda_b = -1/2 $ helicity
amplitudes for the $t\to W^{+}b$ decay mode. For the CP-conjugate case, there
is an analogous function and tests for $\bar{t} \to W^{-} \bar{b}$ decay. These
results make use of W-boson longitudinal-transverse interference.
