Giorgio Lando

Another relation is strictly connected to parthood: the relation that connects many things to a single thing that includes whatever is in the many things and nothing extraneous to them; this many-one relation can be dubbed composition.

The thesis is that there is a single, general, exhaustive theory of parthood and composition. This theory, usually called Classical Extensional Mereology

(a) parthood is transitive (if a first thing is part of a second thing, and this second thing is part of a third thing, then the first thing is part of the third as well);