回溯

回溯	huí sù	to recall / to look back upon
回	huí	to circle / to go back / to turn around / to answer / to return / to revolve / Hui ethnic group (Chinese Muslims) / time / classifier for acts of a play / section or chapter (of a classic book)
回	huí	to curve / to return / to revolve
回	huí	variant of 回
溯	sù	to go upstream / to trace the source
溯	sù	variant of 溯