Nobody answers? My 2 cents then...
By removing 3H20, each composed of one O and the only two H on a nearby C, you can get the central C6 of the trimer. It resembles the three acetylenes making a benzene. But that's all: this intermediate has still thirty H which must all vanish to get the fullerene, so this can't be the last step.
Hope someone else will jump in...