  It has been open for years to clarify the relationship between two smooth
4-manifolds invariants, the shadow model (motivated by statistical mechanics
[Tur91]) and the simplicial Crane-Yetter model (motivated by topological
quantum field theory [CY93]), both of which degenerate to the 3D
Witten-Reshetikhin-Turaev model in a special case. Despite the seeming
difference in their origins and formal constructions, we show that they are in
fact equal.
  Along the way, we sketch a dictionary between the shadow model and the
Crane-Yetter model, provide a brief survey to the shadow construction a la
Turaev, and suggest once again that the semisimple models have reached their
limits.
