Mirka Miller's Combinatorics Webinar Series - Revision history

Mabreu: /* Upcoming Talks: */

2026-10-01T13:36:04Z

‎Upcoming Talks:

Mabreu at 13:34, 1 October 2026

2026-10-01T13:34:29Z

Cristina2: /* Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia) */

2026-09-17T12:43:01Z

‎Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia)

Cristina2: /* Previous Talks */

2026-09-17T12:41:55Z

‎Previous Talks

Cristina2: /* Upcoming Talks: */

2026-09-17T12:37:40Z

‎Upcoming Talks:

Mabreu: /* Upcoming Talks: */

2026-09-16T08:31:06Z

‎Upcoming Talks:

Mabreu at 09:40, 14 September 2026

2026-09-14T09:40:09Z

Mabreu at 09:37, 14 September 2026

2026-09-14T09:37:55Z

Mabreu at 09:36, 14 September 2026

2026-09-14T09:36:18Z

Mabreu at 09:33, 14 September 2026

2026-09-14T09:33:44Z

← Older revision		Revision as of 13:36, 1 October 2026
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	[https://drive.google.com/file/d/1LsRSu1igRFX9J6mJs5oGqU34nUDM5_zI/view?usp=sharing https://drive.google.com/file/d/1LsRSu1igRFX9J6mJs5oGqU34nUDM5_zI/view?usp=sharing]		[https://drive.google.com/file/d/1LsRSu1igRFX9J6mJs5oGqU34nUDM5_zI/view?usp=sharing https://drive.google.com/file/d/1LsRSu1igRFX9J6mJs5oGqU34nUDM5_zI/view?usp=sharing]
		+
		+	Meet Link: [https://meet.google.com/kgc-uwpc-ngp https://meet.google.com/kgc-uwpc-ngp]

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← Older revision		Revision as of 13:34, 1 October 2026
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	==Upcoming Talks:==		==Upcoming Talks:==

		+	=== Giuseppe MAZZUOCCOLO (UniMoRe - Italy) - Disproving the Petersen Coloring Conjecture: Theoretical Analysis and an Infinite Family of Counterexamples ===



		+	'''Date:''' October 21, 2026'''
		+
		+	'''Time''' 17:00 (CET)
		+
		+	''' Speaker: Giuseppe MAZZUOCCOLO (Università di Modena e Reggio Emilia - Italy)'''
		+
		+	''' Title: Disproving the Petersen Coloring Conjecture: Theoretical Analysis and an Infinite Family of Counterexamples'''
		+
		+	'''Abstract: ''' In 1988, Jaeger conjectured that every bridgeless cubic graph G admits a Petersen coloring; that is, a map E(G) → E(P) mapping any two adjacent edges of G to two adjacent edges of the Petersen graph P. In this talk, we begin with a brief introduction to this problem and its deep implications for several famous, long-standing open problems in graph theory. We then recall recent breakthroughs, starting from July 2026, when a 68-vertex counterexample was announced on X, followed shortly by Putman’s two non-isomorphic 112-vertex counterexamples
		+	relying solely on computer-assisted verification. Mainly, we present two counterexamples of order 52, currently the smallest known, and provide the first purely theoretical proof explaining why they do not admit a Petersen coloring. Moreover, we show an infinite family of cyclically 4-edge-connected cubic graphs without a Petersen coloring for every even order at least 60. Additionally, through computational verification, we prove that any counterexample must have order at least 40. Finally, we show that our counterexamples provide a negative answer to other
		+	related problems.
		+
		+	Join work with J. Goedgebeur, J. Jooken, E. Macajova, D. Mattiolo, N. Ulyanov
		+
		+	[https://drive.google.com/file/d/1LsRSu1igRFX9J6mJs5oGqU34nUDM5_zI/view?usp=sharing https://drive.google.com/file/d/1LsRSu1igRFX9J6mJs5oGqU34nUDM5_zI/view?usp=sharing]

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@@ Line 25: / Line 25: @@
 ===Talk 55: Chordal graphs and generalizations - Mónica REYES===
@@ Line 52: / Line 50: @@
 ---
 ===Talk 54: Biregular Cages - György KISS===

← Older revision		Revision as of 12:41, 17 September 2026
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	==Previous Talks==		==Previous Talks==
		+
		+	===Talk 55: Chordal graphs and generalizations - Mónica REYES===
		+
		+
		+	=== <big> '''Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia)'''</big> ===
		+
		+
		+	'''Date:''' September 16, 2026'''
		+
		+	'''Time''' 17:00 (CET)
		+
		+	''' Speaker: Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia) '''
		+
		+	''' Title: On Chordal Ring, Multi-ring and Mixed Graphs, and Three-Quarters Circulant Digraphs'''
		+
		+	'''Abstract: ''' Chordal ring graphs are a well-known family of graphs used to model interconnection networks. In this talk, we consider two families of graph and digraph structures related to circulant networks.
		+	First, we study chordal multi-ring, chordal ring mixed, and chordal multi-ring mixed graphs, which generalize the classical chordal ring graphs. Using plane tessellations, we obtain the maximum number of vertices for a given diameter. We also study these graphs as lift graphs over Abelian groups and obtain closed formulas for their spectra.
		+
		+	We then introduce a new family of three-quarters circulant digraphs associated with the cyclic group (\mathbb{Z}_N). Restricting the admissible combinations of two generators to three coordinate sectors gives a new distance-like function. The same geometric approach based on tessellations allows us to obtain Moore-type upper bounds for the order/diameter problem and construct infinite families with prescribed diameter. We give constructions for both even and odd diameters and discuss the maximum possible order.
		+
		+	Join work with Cristina Dalfó and Miquel Àngel Fiol
		+
		+	'''Video:''' [https://drive.google.com/file/d/1r8CL2X5RYdzUvbxxBoXxKVPpCPM2zEjD/view?usp=drive_link https://drive.google.com/file/d/1r8CL2X5RYdzUvbxxBoXxKVPpCPM2zEjD/view?usp=drive_link]
		+
		+	'''Slides:''' [https://drive.google.com/file/d/1eKVRqY7Up3sb4bOS3yVL2ZJxpNBjFX6r/view?usp=drive_link https://drive.google.com/file/d/1eKVRqY7Up3sb4bOS3yVL2ZJxpNBjFX6r/view?usp=drive_link]
		+
		+	'''Link:''' [https://teams.microsoft.com/l/meetup-join/19%3ameeting_NWM1ZTFhY2MtN2U1MS00ODg2LTgyZmItZTQwNmRmMTI4ODA2%40thread.v2/0?context=%7b%22Tid%22%3a%22fe8d7662-ab03-44d3-8787-fd718b76b5dd%22%2c%22Oid%22%3a%222b443e8c-3de6-43e0-87dc-970e1b830292%22%7d https://teams.microsoft.com/l/meetup-join/19%3ameeting_NWM1ZTFhY2MtN2U1MS00ODg2LTgyZmItZTQwNmRmMTI4ODA2%40thread.v2/0?context=%7b%22Tid%22%3a%22fe8d7662-ab03-44d3-8787-fd718b76b5dd%22%2c%22Oid%22%3a%222b443e8c-3de6-43e0-87dc-970e1b830292%22%7d]
		+
		+
		+	---
		+

← Older revision		Revision as of 12:37, 17 September 2026
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−	~~=== <big> '''Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia)'''</big> ===~~
−
−
−
−
−	~~'''Date:''' September 16, 2026'''~~
−
−	~~'''Time''' 17:00 (CET)~~
−
−	~~''' Speaker: Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia) '''~~
−
−	~~''' Title: On Chordal Ring, Multi-ring and Mixed Graphs, and Three-Quarters Circulant Digraphs'''~~
−
−	'''Abstract: ''' Chordal ring graphs are a well-known family of graphs used to model interconnection networks. In this talk, we consider two families of graph and digraph structures related to circulant networks.
−	First, we study chordal multi-ring, chordal ring mixed, and chordal multi-ring mixed graphs, which generalize the classical chordal ring graphs. Using plane tessellations, we obtain the maximum number of vertices for a given diameter. We also study these graphs as lift graphs over Abelian groups and obtain closed formulas for their spectra.
−
−	We then introduce a new family of three-quarters circulant digraphs associated with the cyclic group (\mathbb{Z}_N). Restricting the admissible combinations of two generators to three coordinate sectors gives a new distance-like function. The same geometric approach based on tessellations allows us to obtain Moore-type upper bounds for the order/diameter problem and construct infinite families with prescribed diameter. We give constructions for both even and odd diameters and discuss the maximum possible order.
−
−	~~Join work with Cristina Dalfó and Miquel Àngel Fiol~~
−
−
−
−	'''Link:''' [https://teams.microsoft.com/l/meetup-join/19%3ameeting_NWM1ZTFhY2MtN2U1MS00ODg2LTgyZmItZTQwNmRmMTI4ODA2%40thread.v2/0?context=%7b%22Tid%22%3a%22fe8d7662-ab03-44d3-8787-fd718b76b5dd%22%2c%22Oid%22%3a%222b443e8c-3de6-43e0-87dc-970e1b830292%22%7d https://teams.microsoft.com/l/meetup-join/19%3ameeting_NWM1ZTFhY2MtN2U1MS00ODg2LTgyZmItZTQwNmRmMTI4ODA2%40thread.v2/0?context=%7b%22Tid%22%3a%22fe8d7662-ab03-44d3-8787-fd718b76b5dd%22%2c%22Oid%22%3a%222b443e8c-3de6-43e0-87dc-970e1b830292%22%7d]

@@ Line 24: / Line 24: @@
 '''Date:''' September 16, 2026'''
-'''Time''' 18:00 (CET)
+'''Time''' 17:00 (CET)
 ''' Speaker: Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia) '''

← Older revision		Revision as of 09:40, 14 September 2026
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	ID de reunión: 897 2536 7001 (for the next talk on May 20, 2026)-->		ID de reunión: 897 2536 7001 (for the next talk on May 20, 2026)-->

−	'''Meeting link:''' ~~[http://meet.google.com/fcf-chxj-dvd http://meet.google.com/fcf-chxj-dvd] (ONLY FOR THE NEXT TALK on June 17, 2026)~~	+	'''Meeting link:''' See below under '''Upcoming Talks'''

@@ Line 496: / Line 496: @@
-=== Talk 35: Ruy Fabila Monroy (Math Department, CINVESTAV, México)  ===
+=== Talk 35: Graphs with non-induced automorphisms of its token graph - Ruy Fabila Monroy (Math Department, CINVESTAV, México)  ===
@@ Line 521: / Line 521: @@
-=== Talk 34: Francesca Merola (Roma Tre University, Italy)  ===
+=== Talk 34: Banff designs: difference methods for coloring incidence graphs -  Francesca Merola (Roma Tre University, Italy)  ===
@@ Line 543: / Line 543: @@
-=== Talk 33: James Tuite (Open University, UK)  ===
+=== Talk 33: Visibility in Graphs - James Tuite (Open University, UK)  ===

@@ Line 274: / Line 274: @@
-===Talk 45: Alexander Gavrilyuk (University of Memphis) ===
+===Talk 45: Non-existence of some Moore Cayley digraphs - Alexander Gavrilyuk (University of Memphis) ===
 '''Date: Wednesday, September 24, 2025'''
@@ Line 299: / Line 299: @@
-=== Talk 44: Federico Romaniello (UNIBAS - Italy) ===
+=== Talk 44: Hamiltonian cycles and perfect matchings: exploring special properties in cubic graphs - Federico Romaniello (UNIBAS - Italy) ===
 '''Date: Wednesday, June 18, 2025'''
@@ Line 322: / Line 322: @@
-=== Talk 43: Isabel Hubard (UNAM - Mexico) ===
+=== Talk 43: Graphs and Groups for Constructing Abstract Polytopes - Isabel Hubard (UNAM - Mexico) ===
 '''Date: Wednesday, May 21, 2025'''
@@ Line 345: / Line 345: @@
-=== Talk 42: Kolja Knauer (Universitat de Barcelona) ===
+=== Talk 42: Coloring Minimal Cayley Graphs - Kolja Knauer (Universitat de Barcelona) ===
 '''Date: Wednesday, April 16, 2025'''
@@ Line 368: / Line 368: @@
-=== Talk 41: Adriana Hansberg (UNAM - Mexico) ===
+=== Talk 41: Graphs with constant link and induced Turán numbers - Adriana Hansberg (UNAM - Mexico) ===
 '''Date: Wednesday March 19, 2025'''

@@ Line 17: / Line 17: @@
-=== <big> '''György KISS  (Eötvös Loránd University) - Biregular Cages'''</big> ===
+=== <big> '''Mónica A. Reyes (Universitat de Lleida, Igualada (Barcelona), Catalonia)'''</big> ===
-'''Date:''' Originally programmed for May 20, 2026 for technical issues it was rescheduled for '''July 15, 2026'''
 '''Time''' 17:00 (CET)
@@ Line 41: / Line 71: @@
 ----
 ===Talk 53: Graphs with bounded diameter/girth ratio - Štefania Glevická===