“…The final problem is about the Bollobás-Riordan polynomial R G (x, y, z). Most of the known results about this polynomial, particularly its combinatorial interpretations, do not apply to the full 3-variable polynomial R G (x, y, z), but rather to its 2-variable specialisation x γ(G)/2 R G (x + 1, y, 1/ √ xy) (see, for example, [7,12,16,19,23,24,29] 4.9. The Penrose polynomial as a Tutte polynomial.…”