y2001p8q7 part b It seems to me that you can guarentee a_t+1 will not terminate when f does not terminate; and as the question emphasizes `safety' it's probably best to say no more. So do you really get 5 marks for writing down not f# => not a_{t+1}# or have I missed something big? -- Crispin This email account will die soon - please use crispin@cantab.net instead!