  Lattice protein models, as the Hydrophobic-Polar (HP) model, are a common
abstraction to enable exhaustive studies on structure, function, or evolution
of proteins. A main issue is the high number of optimal structures, resulting
from the hydrophobicity-based energy function applied. We introduce an
equivalence relation on protein structures that correlates to the energy
function. We discuss the efficient enumeration of optimal representatives of
the corresponding equivalence classes and the application of the results.
