def veins_menors_1(g, n):
    cjt_vm = set()
    for m in g.neighbors(n):
        if m < n:
            cjt_vm.add(m)
    return cjt_vm

def veins_menors_2(g, n):
    vm = filter(lambda m: m < n, g.neighbors(n))
    cjt_vm = set(vm)
    return cjt_vm

def veins_menors_3(g, n):
    cjt_vm = {m for m in g.neighbors(n) if m < n}
    return cjt_vm

# Tria la solució que vulguis provar
veins_menors = veins_menors_1
# veins_menors = veins_menors_2
# veins_menors = veins_menors_3