The long-range forces between holes in an antiferromagnet are due to magnon exchange. The one-magnon exchange potential between two holes is proportional to cos(2 ϕ)/<Emphasis Type="Bold">r <Superscript>2</Superscript> where <Emphasis Type="Bold">r is the distance vector of the holes and ϕ is the angle between <Emphasis Type="Bold">r and an axis of the square crystal lattice....</emphasis></emphasis></superscript></emphasis>