For more background you may want to read the article on Mereology in the online Stanford Encyclopedia of Philosophy at https://plato.stanford.edu/entries/mereology/

which also has an article on Medieval Mereology at https://plato.stanford.edu/entries/mereology-medieval/

Dear Hendrika, 

Thank you for your advisory, I shall read both sites.

Best.

The prominent American philosopher David Lewis used mereology in some of his papers.  All David's papers are available online.  I think you can find them there.

Dear Brooks, thanks a lot for your time to answer.

I will search about David Lewis.

best from Costa Rica

Recently, I found some reference to mereology in Brentano work, in a work of Smith

http://ontology.buffalo.edu/smith/book/austrian_philosophy/CH3.pdf