## Pairs of states

The second moment matrix is also the connectivity matrix for pairs of states discussed in Sec. 3.4, just as the third moment matrix corresponds to triples of states, and so on. No less than restrictions on possible pairs of sequences implied by zero variance, observation of the same limitations in practice can serve as an indicator of zero variance, and consequently of a surjective rule.

Harold V. McIntosh

E-mail:mcintosh@servidor.unam.mx