I'm not sure if I'm understanding it correctly - for my mother to be the common ancestor of the set consisting of me and my mother, is it necessary for my mothe

I'm not sure if I'm understanding it correctly - for my mother to be the common ancestor of the set consisting of me and my mother, is it necessary for my mother to be her own ancestor? I don't think a person is considered their own ancestor in the common usage of the term. Maybe I'm just being pedantic - the numerical examples make more sense to me since any number can be its own factor.