Caterpillar decomposition conjecture for fully leafed Penrose subtrees

Let TT be a fully leafed Penrose subtree. A Penrose tree is saturated if n1(T)=LP2(n(T))n_{1}(T)=\overline{L_{P2}}(n(T)), where LP2(n)=8n/17+b\overline{L_{P2}}(n)=8n/17+b is the unique linear upper bound described in the source, and an appendix is a fully leafed induced subtree whose derived subtree contains precisely one leaf of TT-degree 22 and at most two cells of TT-degree 33. Caterpillar decomposition conjecture.

(i) If TT is saturated, then TT is a caterpillar.

(ii) If TT is non-saturated, then there exist a saturated caterpillar T1T_1 and an appendix T2T_2 such that

T=T1T2.T=T_1\diamond T_2.

This conjecture proposes that saturated fully leafed Penrose subtrees are exactly caterpillars, while every non-saturated one is obtained by grafting an appendix onto a saturated caterpillar. The source gives this as a formalization of observed structures; no resolution is stated.

Sources & referencesView supporting material

Primary source

Carole Porrier, Alain Goupil and Alexandre Blondin Massé, “The Leaf Function of Penrose P2 Graphs”, arXiv:2312.08262 (2025).

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