The original fair partition (spicy chicken) question, posed in 2006, asks if given any positive integer n, every planar convex region can be cut into n convex pieces all of same area and perimeter. After a long series of developments, the question was fully answered in the affirmative in 2018 by Avvakumov, Akopyan and Karasev. The results they obtained are far more general than for area-perimeter.
Definition: a spiral polygon is a simple polygon whose boundary chain contains exactly one concave subchain. We can classify the points on the boundary of a closed planar region as either convex or concave depending on where the center of curvature lies. By generalization, we can define a spiral region which has only one continuous stretch of concave points on its boundary.
Question: For any n, an every planar spiral region be cut into n spiral regions all of the same area and perimeter?
For n = 2, the answer seems "yes". We now try to prove this.
Proof: We use intermediate value theorem (as was done in the n=2 case of the basic fair partition question). We only need to show that there is a continuum of cuttings of the spiral planar region S into 2 spiral regions of same perimeter (not area) and thereafter, we can always say that due to continuity, at least one partition in the continuum also yields 2 equal area pieces.
For every point P on the boundary of S, there is another boundary point Q such that the perimeter of S is divided into 2 equal portions by P and Q. Case 1: If P is somewhere on the concave portion of S, Q is not on this concave portion (easy to see) whereas
Case 2: if P is not on the concave portion, Q may or may not be on the concave portion.
(1) If both P and Q are not on the concave portion, P can always be connected to Q with a curve such that S is divided into 2 sprial regions (easy to see).
(2) If one of P and Q are on the concave portion, we assume without loss of generality, that P is on the non-convex portion of the boundary. Now, it seems clear that the two points can be joined by either a straight line or with a suitable curve such that the two resulting pieces are both spiral. Indeed, If P and Q are mutually visible thru interior of S, we connect P and Q with a straight line; then, the two resulting pieces will obviously have one concave portion each and these portions join at Q in S (so both are spiral); else (if P and Q are not mutually visible), we connect P and Q with a dividing curve that has to meet the concave portion of S at Q at a tangent and should also be bent suitably.
I am not sure about this but our proof of the spicy chicken problem for values of n that are powers of 2 (https://www.ias.ac.in/article/fulltext/pmsc/122/03/0459-0467) *might* generalize for the above spiral version of the question as well.
A Weaker version: If we slightly relax the definition of spiral region to one with *at most one concave subchain* thereby making convex regions trivially spiral, can we say that for any n, we can cut any spiral region into n spiral (in this relaxed sense) regions of same area and perimeter?
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