Puzzle 4. Just to give an "applied" example:

In rational continuum mechanics, Truesdell starts defining a poset, and then a Boolean algebra, to construct a "universe of bodies" in which to define mechanics (see Clifford Truesdell, A first course in rational continuum mechanics).

In rational continuum mechanics, Truesdell starts defining a poset, and then a Boolean algebra, to construct a "universe of bodies" in which to define mechanics (see Clifford Truesdell, A first course in rational continuum mechanics).