function AFf = checkAF(f)% Evaluate the `computation tree logic (CTL)` expression "AF f". %% Syntax:%   "AFf = checkAF(f)"%% Description:%   Given a finite-state transition system and its reverse transition system%   stored in the global variables "GLOBAL_TRANSITION" and%   "GLOBAL_REV_TRANSITION" and a "region" object "f", compute the region%   corresponding to the CTL expression "AF f".%% Implementation:%   Use the CTL identity %%   "AF f = ~(EG ~f)"%% See Also:%   region,auto2xsys,reach,findSCCf,checkAG,checkAR,checkAU,checkAX,%   checkEF,checkEG,checkER,checkEU,checkEXAFf = ~checkEG(~f);return