Reciprocal and non-reciprocal variant edges. Two classes of variant edges in the interval-adjacency graph. Reciprocal variants are pairs of variant edges incident to the same four interval edges (I
, Ip+1, I
, Iq+ 1), while non-reciprocal variants are the cases where only a single variant edge is incident to the four interval edges defined by the variant edge. A trivial reciprocal variant has equal inferred multiplicities: μ(A) = μ(A'), μ(I
) = μ(Ip+1), and μ(I
) = μ(Iq+1).