21. Shortest paths in polygons

a. Setup and motivation
b. Structure: polygonal path through reflex vertices
c. Greedy improvement
d. Crosses any diagonal at most once.
e. Sleeve: triangles dual to path in dual tree
f. Funnel structure: tail, apex, body
g. Extending a funnel across a triangle in O(1) amortized time
h. Polygons with holes?