English is my second language, and I'm having trouble understanding the structure of the highlighted sentence down below.
"In his description of how he became a master riverboat pilot in Life on the Mississippi, Mark Twain gave us a vision of learning that incorporates basic skills and the capacity to go beyond them. Twain learns how to navigate the river at young age, learning every shoal, snag, and sandbar, which are the basic skills. But no sooner has he memorized their locations and peculiarities than he has to modify or forget them, and learn other spots, for the river never stops changing its course. Twain must simultaneously remember the reality of what exists in the river and imagine how different forces and conditions are likely to change it. He can never know the river completely or certainly because knowledge about the river is always temporary."
I know that the sentence is inverted, but I don't understand the use of 'than'.