Compact hyperbolic tetrahedra with non
... Lemma 2 Suppose that three planes Pv1 , Pv2 , Pv3 intersect pairwise in H3
with non-obtuse dihedral angles α, β, and γ. Then, Pv1 , Pv2 , Pv3 intersect at
a vertex in H3 if and only if α + β + γ ≥ π. The planes intersect in H3 if and
only if the inequality is strict.
Proof: The planes intersect in ...