Dear Sam, now the timing looks more optimistic, 111.858195 seconds (31.43 k allocations: 1.442 MB, 0.00% gc time) 267.895365 seconds verification succeeded
I have about 2.5-folds speed-up with threads, which is better. It did not help me with my original problem though. Nevertheless, thank you very much for discussion. Best wishes, Tomas
