[Tutor] Confusion about definition of proper subset in python set

[Manprit Singh]

Dear sir ,

Consider explanation given about  set < other in python official
documentation

Test whether the set is a proper subset of *other*, that is, set <= other
and set != other.

This confuses me actually.

set <= other   and set != other , how it is possible at same time ?

As far as i know, if S is a set and ss is its proper subset, then ss is
strictly contained in S and necessarily excludes at least one member of S.

Need some light on it.

Regards
Manprit Singh