Generic 2:2 relation for natural parameters of degenerate tetrahedra

Let α,β,γ,δ,ςR\alpha,\beta,\gamma,\delta,\varsigma\in\mathbb R satisfy

α+β+γ+δ>α+β+γ+δ,αβγδ>0,|\alpha|+|\beta|+|\gamma|+|\delta|>|\alpha+\beta+\gamma+\delta|,\qquad \alpha\beta\gamma\delta>0,

and let ϱ+(α,β,γ,δ)\varrho_+(\alpha,\beta,\gamma,\delta) denote the unique positive root of the discriminant quadratic described in the surrounding discussion. Generic 2:2-relation conjecture. The equations referenced in the source generically define a 2 ⁣: ⁣22\!:\!2 relation between the natural parameters of degenerate tetrahedra and the semi-algebraic set

{α,β,γ,δ,ςRα+β+γ+δ>α+β+γ+δ, αβγδ>0, ς>ϱ+(α,β,γ,δ)}.\left\{\alpha,\beta,\gamma,\delta,\varsigma\in\mathbb R\mathrel{\bigm|}|\alpha|+|\beta|+|\gamma|+|\delta|>|\alpha+\beta+\gamma+\delta|,\ \alpha\beta\gamma\delta>0,\ \varsigma>\sqrt{\varrho_+(\alpha,\beta,\gamma,\delta)}\right\}.

The conjecture describes the generic multiplicity of the parameter correspondence in the region where the preceding analysis predicts three real roots.

Sources & referencesView supporting material

Primary source

Timothy F. Havel, “An Extension of Heron's Formula to Tetrahedra, and the Projective Nature of Its Zeros”, arXiv:2204.08089 (2025).

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