Full Idea
Set inclusion is sharply distinguished from set membership (as the set of Greeks is found to be included in, but not a member of, the set of men).
Gist of Idea
The set of Greeks is included in the set of men, but isn't a member of it
Source
José A. Benardete (Metaphysics: the logical approach [1989], Ch.13)
Book Reference
Benardete,José A.: 'Metaphysics: The Logical Approach' [OUP 1989], p.90