  In terms of the relational approach to space-time geometry and physical
interactions, we show that the Dirac equation for a free fermion in the
momentum representation can be obtained starting from a binary system of
complex relations (BSCR) between elements of two abstract sets. With the
derivation performed we show that the 4-dimensional pseudo-Euclidean momentum
space is not needed a priori but naturally emerges from considerations of
rather general character (2-spinor algebra). A bispinor wave function is
constructed for a fermion with positive energy and an arbitrary distribution of
momenta. Special attention is paid to physical assumptions that should be made
to enable the construction.
