  The Kuchar observables notion is shown to apply only to a limited range of
theories. Relational mechanics, slightly inhomogeneous cosmology and
supergravity are used as examples that require further notions of observables.
A suitably general notion of A-observables is then given to cover all of these
cases. `A' here stands for `algebraic substructure'; A-observables can be
defined by association with each closed algebraic substructure of a theory's
constraints. Both constrained algebraic structures and associated notions of
A-observables form bounded lattices.
