  We suggest a mechanism whereby the three generations of quarks and leptons
correspond to surface modes in a five-dimensional theory. These modes arise
from a nonlinear fermion dispersion relation in the extra dimension, much in
the same manner as fermion surface modes in a topological insulator or lattice
implementation of domain wall fermions. We also show that the topological
properties can persist in a deconstructed version of the model in four
dimensions.
