Характеристический конус

D_T = S₁ ∪ S₂ ∪ S₃

S₁ = {(x, t): x ∈ , t = 0}

S₂ = {(x, t): |x − x₀| ≤ a(t₀ − T), t = T}

S₃ = {(x, t): 0 ≤ t ≤ T, |x − x₀| = a(t₀ − t)}