Lattice path matroids: enumerative aspects and Tutte polynomials
Journal of Combinatorial Theory Series A
Maintaining the spirit of the reflection principle when the boundary has arbitrary integer slope
Journal of Combinatorial Theory Series A
Combinatorial Enumeration
A solution to the tennis ball problem
Theoretical Computer Science - In memoriam: Alberto Del Lungo (1965-2003)
Note: Simple formulas for lattice paths avoiding certain periodic staircase boundaries
Journal of Combinatorial Theory Series A
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We count the number of lattice paths lying under a cyclically shifting piecewise linear boundary of varying slope. Our main result can be viewed as an extension of well-known enumerative formulae concerning lattice paths dominated by lines of integer slope (e.g. the generalized ballot theorem). Its proof is bijective, involving a classical ''reflection'' argument. Moreover, a straightforward refinement of our bijection allows for the counting of paths with a specified number of corners. We also show how the result can be applied to give elegant derivations for the number of lattice walks under certain periodic boundaries. In particular, we recover known expressions concerning paths dominated by a line of half-integer slope, and some new and old formulae for paths lying under special ''staircases.''