#35 Detailed explanation for -mt=on with LZMA2

[Sworddragon]

DOCS/MANUAL/switches/method.htm says that on LZMA 1 thread for x[1, 3] and 2 threads for x[5,7,9] are save for the maximum compression rate. I would like to know if -mmt is set to on how many threads it will choose. Is it maybe safe (maximum compression rate) in combination with LZMA2?