  It is proved that in a distinguishing spacetime the horismos relation
E^+=J^+\I^+ generates the causal relation J^+. In other words two causally
related events are joined by a chain of horismotically related events, or
again, the causal relation is the smallest transitive relation containing the
horismos relation. The result is sharp in the sense that distinction can not be
weakened to future or past distinction. Finally, it is proved that a spacetime
in which the horismos relation generates the causal relation is necessarily
non-total imprisoning.
