  Difference calculus compatible with polynomials (i.e., such that the divided
difference operator of first order applied to any polynomial must yield a
polynomial of lower degree) can only be made on special lattices well known in
contemporary $q-$calculus. Orthogonal polynomials satisfying difference
relations on such lattices are presented. In particular, lattices which are
dense on intervals ($|q|=1$) are considered.
