A context-freegrammar(CFG)in GreibachNormalForm coincides,in anothernotation,witha system of guarded recursion equations in Basic Process Algebra. Hence to each CFG a process can be assignedas solution,which has as its set of finite tracesthe context-freelanguage (CFL)determinedby that CFG. While the equality problem for CFL's is unsolvable, the equality problem for the processes determined by CFG's turnsout to be solvable. Hereequality on processes is given by a model of process graphs modulo bisimulation equivalence. The proof is given by displaying a periodic structure of the process graphs determinedby CFG's.As a corollaryof theperiodicitya short proofof the solvabilityof the equivalenceproblemfor simplecontext-freelanguagesis given.
Jos C. M. Baeten, Jan A. Bergstra, Jan Willem Klop