  Interest on 2 + 1 dimensional electron systems has increased considerably
after the realization of novel properties of graphene sheets, in which the
behaviour of electrons is effectively described by relativistic equations.
Having this fact in mind, the following problem is studied in this work: when a
spin 1/2 particle is constrained to move on a curved surface, is it possible to
describe this particle without giving reference to the dimensions external to
the surface? As a special case of this, a relativistic spin 1/2 particle which
is constrained to move on a 2 + 1 dimensional hypersurface of the 3 + 1
dimensional Minkowskian spacetime is considered, and an effective Dirac
equation for this particle is derived using the so-called thin layer method.
Some of the results are compared with those obtained in a previous work by M.
Burgess and B. Jensen.
