Conformal Spaces. Geometry Seminar, Department of Mathematics, University of Toronto, Canada, February 1979

Cone Preserving Mappings. Workshop in Geometry and Algebra, Technical University of Munich, W. Germany, February 1980

Characterizations of Lorentz Transformations. Geometry Colloquium, Mathematics Institute, University of Hannover, W. Germany, June 1980

Characterizations of Spacetime Transformations. Mathematics Colloquium. York University, Toronto, Canada, February 1983

Characterization Theorems on Metric Vector Spaces. Geometry Seminar, Department of Mathematics, University of Toronto, Canada, September 1985

Some Characterizations of Euclidean Motions. Mathematics Colloquium, University of Oldenburg, W. Germany, November 1985

Transformations Preserving Null Line Sections of a Domain. Mathematics Colloquium, University of Duisburg, W. Germany, November 1985

Mappings Preserving Null Line Sections of a Domain. Mathematics Colloquium, University of Hannover, W. Germany, November 1985

A Characterization of Conformal Metric Vector Space Transformations. Geometry Workshop, Technical University of Munich, W. Germany, November 1985

A Characterization of Conformal Transformations for a Space of Arbitrary Signature Geometry Seminar, University of Rome, Italy, November 1985

Transformations Preserving Null Line Sections of a Domain. University of Florence, Italy, November 1985

Some Beckman-Quarles Type Characterization Problems from Euclidean Geometry. Catholic University of the Sacred Heart, Brescia, Italy, November 1985

Characterizations of Geometric Mappings Under Mild Hypotheses. Geometry Workshop, University of Hamburg, W. Germany, November 1985

Application of Metric Vector Space Geometry to the Derivation of Spacetime Transformations. University of Guelph, Canada, March 1987

Metric Vector Spaces and Spacetime Geometry. University of Winnipeg, Canada, March 1987

Relative Infinity in Geometry and Spacetime Geometry. University of Victoria, Canada, July 1990

Infinite But Not Absolute. Geometry Colloquium, University of Toronto, January 1991

Relative Infinity in Classical Geometry and Relative Infinity in Spacetime Geometry (2 talks). Geometry Workshop, University of Hamburg, Germany, May 1991 (as a visiting Blaschke Professor)

Centres of Triangles. Geometry Colloquium, University of Hamburg, Germany, June 1992

Euclidean Triangle Geometry via Complex Triangle Functions. University of Victoria, Canada, August 1993

A generalization of Napoleon's theorem to n-gons. Geometry Workshop, University of Hamburg, Germany, July 1994

The Universe is 25 Billion Years Old, or How to Get Interesting Physics from Classical Inversive Geometry. Simon Fraser University, Burnaby, Canada, February 1996

Geometry, Computers and the Internet. University of Hamburg, Germany, June 1997

Conformal Minkowski Space. Conference on the Foundations of Geometry, Mathematical Research Institute at Oberwolfach, W. Germany, May 1980

NATO Advanced Study Institute Summer School on "Geometry - von Staudt's Point of View"; Bad Windsheim, W. Germany, July 1980 (no talk)

A Physical Characterization of Conformal Transformations of Minkowski Spacetime. Conference on Combinatorial Geometries and Their Applications, Rome, June 1981

The Beckman-Quarles Theorem in Minkowski Space for a Spacelike Square- Distance Tenth Austrian Conference of Mathematicians, Innsbruck, September 1981

Transformations of de Sitter and Einstein Cylinder Spacetimes Preserving Separation. Conference on the Foundations of Geometry, Mathematical Research Institute at Oberwolfach, W. Germany, October 1982

Transformations Preserving Unit Triangles. Conference on the Foundations of Geometry, Mathematical Research Institute at Oberwolfach, W. Germany, October 1985

Relative Infinity in de Sitter Spacetime Geometry. Combinatorics '86, La Mendola, Italy, July 1986

Spacetime Geometry via Metric Vector Space Models. Annual Meeting of the German Mathematical Association, Berlin, W. Germany, September 1987

A Beckman-Quarles-Type Theorem for Coxeter's Inversive Distance. Conference on the Foundations of Geometry, Mathematical Research Institute at Oberwolfach, W. Germany, December 1988

The Effect of a Relative Infinity on Cosmological Redshifts. Conference on Relativity and Astrophysics, Victoria, Canada, May 1989 (poster)

Relative Infinity in Geometry. Third International Conference on Geometry. Thessaloniki, Greece, May 1991

The Preservation of Causality on FLRW Spacetimes. Geometry Conference in Hamburg, Germany, July 1992

Geometric Centres of Triangles. St. Andrews Colloquium, St Andrews, Scotland, July 1992

Centre Functions for Triangles. Conference on the Foundations of Geometry, Mathematical Research Institute at Oberwolfach, Germany, January 1993

Zeeman's Theorem on Robertson-Walker Spacetimes. Fifth Canadian Conference on General Relativity and Relativistic Astrophysics, Waterloo, Canada, May 1993

A generalization of Napoleon's theorem to n-gons. (poster) International Congress of Mathematicians, Zürich, August 1994