Task: Question Answering
Input (English): Context: Si Renfa's son Si Jifa escaped and continued independent action in another corner of southwest Yunnan. He sent his younger brother Zhaosai to seek pardon from Ming while at the same time he attacked Ming troops in early 1443. However they were defeated and he was forced to flee to Mong Yang. Zhaosai was kept as a hostage and the Ming retreated from Mong Mao. Seeing that Mong Mao was no longer occupied, Si Jifa returned to his father's base of power and began attacking neighboring tribes once again. The third punitive expedition was led by Wang Ji and launched in March 1443. Although the mission was to capture Si Jifa, negotiations on the return of Si Renfa had fallen ill. Ava demanded Ming territory for itself and Hsenwi in return of Si Renfa. Furthermore Ava had made peace with Si Jifa. Therefore, although the Ming army quickly defeated Si Jifa's base of power and captured his family, Si Jifa managed to escape to Mong Yang, and the Ming army decided not to pursue out of consideration of a combined Ava-Hsenwi attack on Ming forces. A compromise was finally reached between Ava and Ming in April 1445. Ava agreed to hand over Si Renfa in return for Ming support in annexing part of Hsenwi's territory. Si Renfa came into Ming custody in August 1445 and was executed in January 1446. 
 Question: Where did Si Renfa have a base of power?
Output (English): mong mao