Fig. 2.

The support triangle Δ(p₁, p₀, p₂) of a short arc Γ (p₁, p₂) is determined by the end-points p₁, p₂ and by the intersection p₀ of the given tangents at the end-points. The sides of the triangle are p₁p₂, p₁p₀ and p₀p₂. Every point p ∈ (p₁, p₂), splits the arc into two smaller ones. The tangent to p cuts the support triangle at points p_a and p_b. The two small arcs have support triangles Δ(p1, p_a , p) and Δ(p, p_b, p₂)