Axioms for Generalized Graphs, Illustrated by a Cantor-Bernstein Proposition. - Joost Engelfriet; Tjalling Gelsema (Acta Informatica, 1998)

Multisets and Structural Congruence of the pi-Calculus with Replication. - Joost Engelfriet; Tjalling Gelsema (Theor. Comput. Sci., 1999)

Structural inclusion in the pi-calculus with replication. - Joost Engelfriet; Tjalling Gelsema (Theor. Comput. Sci., 2001)

A new natural structural congruence in the pi-calculus with replication. - Joost Engelfriet; Tjalling Gelsema (Acta Informatica, 2004)

An exercise in structural congruence. - Joost Engelfriet; Tjalling Gelsema (Inf. Process. Lett., 2007)

The Logic of Aggregated Data. - Tjalling Gelsema (Acta Cybern., 2019)