semilattice (V,≤) is a median semilattice if and only if V is a distributive semilattice, and any three elements of V have an … is well- known (see [1], [2], and [15]): If G = (V,E) is a median graph and z ∈ V, then (V,≤z) is a median semilattice … where ≤z is defined by x ≤z y if and only if x ∈ I(z,y). Conversely, the covering graph of a median semilattice is a median …

aggregate can be endowed with an order structure, namely a structure of median semilattice. …