Pym, D;    Collinson, M;    McDonald, K;      (2015)    Layered graph logic as an assertion language for access control policy models.                   Journal of Logic and Computation , 27  (1)   pp. 41-80.    10.1093/logcom/exv020 <https://doi.org/10.1093/logcom%2Fexv020>.       Green open access