Future horismos
= Future horismos
{title2=$E^+(S)=J^+(S)\setminus I^+(S)$}
The <future horismos> is the part of the <causal future> outside the <chronological future>. For a <compact> set in a <globally hyperbolic spacetime>, it equals the <boundary> of the <chronological future>. Its normal <null geodesic> generators cannot have passed a <conjugate point to a spacelike surface> when the initial set is that surface.