nodes = ["uno","dos","tres","cuatro","cinco","seis"]

pairs = [(i,j) for i in nodes for j in nodes if i!=j]

ARCS = [("uno", "dos"), ("uno", "tres"), ("dos", "tres"), ("dos", "cuatro"),
("tres", "cuatro"), ("tres", "cinco"), ("cuatro", "cinco"),("cuatro","seis"), ("cinco", "seis"), ("dos","uno"), ("tres","uno")]

F = [[mdl.binary_var_dict(ARCS, name= "F")] for p in pairs]

mdl.sum([(F[a][p]) for a in ArcsOut[p[0]]] for p in pairs)