Exactly one-intersecting family
= Exactly one-intersecting family
An exactly one-intersecting family satisfies $|A\cap B|=1$ for every two distinct members. It is nontrivial when the intersection of all its members is empty.
= Exactly one-intersecting family
An exactly one-intersecting family satisfies $|A\cap B|=1$ for every two distinct members. It is nontrivial when the intersection of all its members is empty.