Decompositions of various kinds
of mathematical objects as products or coproducts are considered, and the
uniqueness of these decompositions is discussed. For instance, the following
topological result is proved. Let Δ be the set of formal, simply-connected, rational
homotopy types having finitely generated rational homotopy. Of course, Δ is a
commutative semigroup with respect to the usual product space construction. Then
Δ is a free commutative semigroup.