Folks, there is a weird thing in windows version of luatex (details here: http://tracker.luatex.org/view.php?id=323), not observed in normal lua binary. The following program gives always the same sequence of random numbers, no matter what seed is used. Not observed on linux. Could one check how it behaves on mac or bsd? local rand = math.random local seed = math.randomseed --seed(1) --seed(14) --seed(1414) --seed(141421) seed(314159) co = coroutine.wrap(function() -- If you call seed here, everything is fine -- If you run this loop with no coroutine, everything is fine for i=1, 10 do print(rand()) end end) co() Thanks, Paweł -- Pawe/l Jackowski P.Jackowski@gust.org.pl