  A system of two biased, mutually exclusive random walkers on an infinite 1D
lattice is studied whereby the intrinsic bias of one particle is equal and
opposite to that of the other. The propogator for this system is solved exactly
and expressions for the mean displacement and mean square displacement (MSD)
are found. Depending on the nature of the intrinsic bias, the system's
behaviour displays two regimes, characterised by (i) the particles moving
towards each other and (ii) away from each other, both qualitatively different
from the case of no bias. The continuous-space limit of the propogator is found
and is shown to solve a Fokker-Planck equation for two biased, mutually
exclusive Brownian particles with equal and opposite drift velocity.
