= Spinless fermion t-V chain
{title2=$H=-t\sum_j(c^\dagger_{j+1}c_j+\mathrm{h.c.})+V\sum_jn_jn_{j+1}$}
A <tight binding> chain of one species of <fermions> with nearest-neighbour hopping and density interaction. At half filling and $V/|t|\to+\infty$, minimizing the interaction requires alternating occupied and empty sites. An even periodic chain has two such configurations at $t=0$; finite hopping admixes defects through <virtual hopping>. A finite ring can select <superpositions> rather than one ordered product state. Two uncoupled copies have four limiting ordered choices when each is half filled, without a general claim of exact finite-hopping fourfold <state degeneracy>.
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