  We construct a compact closed category out of any symmetric monoidal category
by freely adding adjoints to its objects. The morphisms of the completion are
defined as string diagrams annotated by objects and morphisms from the original
category. The symmetric monoidal category embeds via a faithful monoidal
functor into its completion, but in contrast to the non-symmetric case, this
embedding is not full. Our construction factors through the Int construction,
which yields another free construction: the free traced monoidal category on a
symmetric monoidal category.
