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math.CO2026
Four-arm polyominoes in Golomb's hierarchy: A complete classification with Lean verification
Angel Ivanov Raychev
We classify the polyominoes obtained by adjoining four straight arms to a single square, allowing zero arm lengths, according to their ability to tile rectangles, half-strips, bent…
math.CO2021
A Generalization of Descent Polynomials
Angel Raychev
The notion of a descent polynomial, a function in enumerative combinatorics that counts permutations with specific properties, enjoys a revived recent research interest due to its…