@article{MTMT:32982788, title = {Boundary-Rigidity of Projective Metrics and the Geodesic X-Ray Transform}, url = {https://m2.mtmt.hu/api/publication/32982788}, author = {Kurusa, Árpád and Ódor, Tibor}, doi = {10.1007/s12220-022-00942-y}, journal-iso = {J GEOM ANAL}, journal = {JOURNAL OF GEOMETRIC ANALYSIS}, volume = {32}, unique-id = {32982788}, issn = {1050-6926}, abstract = {We prove that given a compact convex non-empty domain M in the plane, a function delta: partial derivative M x partial derivative M -> R+ can be extended to a projective metric d on M if and only if delta(P, R) +delta(Q, S) - delta(P, S) - delta(Q, R) > 0 for any convex quadrangle square(PQRS) inscribed in partial derivative M. Moreover, this extension is unique.}, keywords = {Rigidity; X-ray transform; projective metric}, year = {2022}, eissn = {1559-002X}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:31371509, title = {Finding Needles in a Haystack}, url = {https://m2.mtmt.hu/api/publication/31371509}, author = {Kurusa, Árpád}, doi = {10.1007/s00454-020-00217-9}, journal-iso = {DISCRETE COMPUT GEOM}, journal = {DISCRETE AND COMPUTATIONAL GEOMETRY}, volume = {65}, unique-id = {31371509}, issn = {0179-5376}, abstract = {Convex polygons are distinguishable among the piecewise $C^\infty$ convex domains by comparing their visual angle functions on any surrounding circle. This is a consequence of our main result, that every segment in a $C^\infty$ multi\-curve can be reconstructed from the masking function of the multicurve given on any surrounding circle.}, year = {2021}, eissn = {1432-0444}, pages = {470-475}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:31290416, title = {Curvature in Hilbert Geometries}, url = {https://m2.mtmt.hu/api/publication/31290416}, author = {Kurusa, Árpád}, journal = {International Journal of Geometry}, volume = {9}, unique-id = {31290416}, issn = {2247-9880}, year = {2020}, eissn = {2247-9880}, pages = {85-94}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:31681702, title = {Euler's ratio-sum theorem revisited}, url = {https://m2.mtmt.hu/api/publication/31681702}, author = {Kurusa, Árpád and Kozma, József}, journal-iso = {Glob. J. Adv. Res. Cl. Mod. Geom.}, journal = {GLOBAL JOURNAL OF ADVANCED RESEARCH ON CLASSICAL AND MODERN GEOMETRIES}, volume = {9}, unique-id = {31681702}, year = {2020}, eissn = {2284-5569}, pages = {83-89}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:31407382, title = {Tiling a circular disc with congruent pieces}, url = {https://m2.mtmt.hu/api/publication/31407382}, author = {Kurusa, Árpád and Lángi, Zsolt and Vígh, Viktor}, doi = {10.1007/s00009-020-01595-3}, journal-iso = {MEDITERR J MATH}, journal = {MEDITERRANEAN JOURNAL OF MATHEMATICS}, volume = {17}, unique-id = {31407382}, issn = {1660-5446}, abstract = {In this note we prove that any monohedral tiling of the closed circular unit disc with $k \leq 3$ topological discs as tiles has a $k$-fold rotational symmetry. This result yields the first nontrivial estimate about the minimum number of tiles in a monohedral tiling of the circular disc in which not all tiles contain the center, and the first step towards answering a question of Stein appearing in the problem book of Croft, Falconer and Guy in 1994.}, year = {2020}, eissn = {1660-5454}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606; Lángi, Zsolt/0000-0002-5999-5343} } @article{MTMT:30795464, title = {Hilbert geometries with Riemannian points}, url = {https://m2.mtmt.hu/api/publication/30795464}, author = {Kurusa, Árpád}, doi = {10.1007/s10231-019-00901-5}, journal-iso = {ANN MAT PUR APPL}, journal = {ANNALI DI MATEMATICA PURA ED APPLICATA}, volume = {199}, unique-id = {30795464}, issn = {0373-3114}, year = {2020}, eissn = {1618-1891}, pages = {809-820}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:30358648, title = {Euler’s ratio-sum formula in projective-metric spaces}, url = {https://m2.mtmt.hu/api/publication/30358648}, author = {Kurusa, Árpád and Kozma, József}, doi = {10.1007/s13366-018-0422-6}, journal-iso = {BEITR ALGEBR GEOM}, journal = {BEITRAGE ZUR ALGEBRA UND GEOMETRIE}, volume = {60}, unique-id = {30358648}, issn = {0138-4821}, abstract = {We prove that Euler’s ratio-sum formula is valid in a projective-metric space if and only if it is either elliptic, hyperbolic, or Minkowskian.}, year = {2019}, eissn = {2191-0383}, pages = {379-390}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:30359280, title = {A convex combinatorial property of compact sets in the plane and its roots in lattice theory}, url = {https://m2.mtmt.hu/api/publication/30359280}, author = {Czédli, Gábor and Kurusa, Árpád}, journal-iso = {CAT GEN ALGEBR STRUCT APPL}, journal = {CATEGORIES AND GENERAL ALGEBRAIC STRUCTURES WITH APPLICATIONS}, volume = {11}, unique-id = {30359280}, issn = {2345-5853}, abstract = {K. Adaricheva and M. Bolat have recently proved that if $U_0$ and $U_1$ are circles in a triangle with vertices $A_0,A_1,A_2$, then there exist $j\in\{0,1,2\}$ and $k\in\{0,1\}$ such that $U_{1−k}$ is included in the convex hull of $U_k\cup(\{A_0,A_1,A_2\}∖setminus\{A_j\})$. One could say disks instead of circles. Here we prove the existence of such a $j$ and $k$ for the more general case where $U_0$ and $U_1$ are compact sets in the plane such that $U_1$ is obtained from $U_0$ by a positive homothety or by a translation. Also, we give a short survey to show how lattice theoretical antecedents, including a series of papers on planar semimodular lattices by G. Gr\"atzer and E. Knapp, lead to our result.}, year = {2019}, eissn = {2345-5861}, pages = {57-92}, orcid-numbers = {Czédli, Gábor/0000-0001-9990-3573; Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:30852537, title = {Ceva’s and Menelaus’ theorems in projective-metric spaces}, url = {https://m2.mtmt.hu/api/publication/30852537}, author = {Kurusa, Árpád}, doi = {10.1007/s00022-019-0495-x}, journal-iso = {J GEOM}, journal = {JOURNAL OF GEOMETRY}, volume = {110}, unique-id = {30852537}, issn = {0047-2468}, abstract = {We prove that Ceva’s and Menelaus’ theorems are valid in a projective-metric space if and only if the space is any of the elliptic geometry, the hyperbolic geometry, or the Minkowski geometries. © 2019, The Author(s).}, keywords = {Triangle; Minkowski geometry; Ellipses; Hilbert geometry; Projective metrics; size-ratio}, year = {2019}, eissn = {1420-8997}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} } @article{MTMT:3424053, title = {Conics in Minkowski geometries}, url = {https://m2.mtmt.hu/api/publication/3424053}, author = {Kurusa, Árpád}, doi = {10.1007/s00010-018-0592-1}, journal-iso = {AEQUATIONES MATH}, journal = {AEQUATIONES MATHEMATICAE}, volume = {92}, unique-id = {3424053}, issn = {0001-9054}, year = {2018}, eissn = {1420-8903}, pages = {949-961}, orcid-numbers = {Kurusa, Árpád/0000-0003-3113-9606} }