Everyday actions can be of surprising structural complexity. Such complexity is playfully achieved by humans and may even remain unnoticed unless confronted with patients with apraxia or dementia, in whom this remarkable capacity vanishes. Figure 1 describes key components of an everyday action sequence (tooth cleaning), which may include the action schemas described on the left, lined up from top to bottom, followed by those on the right from bottom to top. This complex action sequence can be broken down into several local complementary sequences (indexed by different colors), which are hierarchically embedded into each other, and one may indeed suggest that there is no strict upper limit for the number of such iterations and embeddings.