Michael Kaminski Chung Kei Wong The Power of the "Always" Operator in First-Order Temporal Logic. 271-281 1996 160 Theor. Comput. Sci. 1&2 db/journals/tcs/tcs160.html#KaminskiW96 http://dx.doi.org/10.1016/0304-3975(95)00108-5