Epireflections in abelian topological groups,
Universita di L'Aquila, December 1979

Some results in abelian group theory,
Universita di L'Aquila, February 1980

Epireflections versus bireflections for topological functors,
Kansas State University, February 1983

Category theory and Pontryagin duality,
Kansas State University, March 1984

Closure operators and epimorphisms in abelian groups and in general,
Kansas State University, April 1985

Closure operators, epimorphisms and Hausdorff objects,
Kansas State University, May 1986

Closure operators, monomorphisms and epimorphisms,
University of Puerto Rico at Mayagüez, February 1987

Compact objects of a closure operator,
Universita di L'Aquila, June 1987

A factorization of the Pumplün-Röhrl connection,
Catholic University of Louvain, July 1987

Closure operators and compactness,
Charles University, Prague, August 1988

Closure operators and compactness,
University of Puerto Rico at Mayagüez, October 1988

Regular closure operators and compactness,
Kansas State University, March 1990

Closure operators and connectedness,
University of Toledo, September 1991

Hereditary closure operators and injectivity
University of Puerto Rico at Mayagüez, February 1992

An approach to a dual or regular closure operators
Universita di L'Aquila, February 1993

Two approaches to the closure, from ``above'' and from ``below'',
University of Puerto Rico at Humacao, February 1994

Connectedness and disconnectedness, a more general approach
Universita di L'Aquila, September 1994

Closure operators with respect to a functor
Interamerican University at Arecibo, April 1996

Connectedness in FTS revisited
University of Puerto Rico at Humacao, February 1998

Connectedness with respect to a closure operator
University of Antwerp, Belgium, March 1998

Connectedness with respect to a closure operator, part II
Kent State University, August 1998

Connectedness, disconnectedness and beyond
University of Puerto Rico at Mayagüez, April 1999

Connectedness with respect to a closure operator, part III
University of Coimbra, Coimbra, Portugal, July 1999

Connectedness: merging the algebraic and the topological approach
University of Puerto Rico at Mayagüez, February 2000

Disconnectedness with respect to a closure operator
University of Bremen, Germany, August 2000

A link between two connectedness notions
Pontificia Universidad Catolica de Puerto Rico, Ponce, February 2003

Separation in a category rivisited
University of Puerto Rico at Cayey, Cayey, February 2004

T1 Separation in a category
University of Puerto Rico at Mayagüez, Mayagüez, February 2005

T1 objects of a closure operator
University of Puerto Rico at Mayagüez, Mayagüez, April 2006

Discrete objects and splitting closure
University of Puerto Rico at Ponce, Ponce, February 2007

A categorical approach to absolute closure
University of Puerto Rico at Rio Piedras, Rio piedras, March 2009

Interior operators and topological connectedness
University of The Azores, Ponta Delgada, March 2010

Interior operators and topological separation
University of Puerto Rico at Mayagüez, Mayagüez, February 2012

A diagram of Galois connectons of functorial topologies
Pontificia Universidad Catolica de Puerto Rico, Ponce, February 2014