uMarked_mergenil++vmergezyxmerge(x,nil)xmerge(nil,y)ymerge(++(x,y),++(u,v))++(x,merge(y,++(u,v)))merge(++(x,y),++(u,v))++(u,merge(++(x,y),v))merge(x,nil)xmerge(nil,y)ymerge(++(x,y),++(u,v))++(x,merge(y,++(u,v)))merge(++(x,y),++(u,v))++(u,merge(++(x,y),v))Marked_merge(++(x,y),++(u,v))Marked_merge(y,++(u,v))Marked_merge(++(x,y),++(u,v))Marked_merge(++(x,y),v)merge(x,nil)xmerge(nil,y)ymerge(++(x,y),++(u,v))++(x,merge(y,++(u,v)))merge(++(x,y),++(u,v))++(u,merge(++(x,y),v))Marked_merge(++(x,y),++(u,v))Marked_merge(y,++(u,v))merge3230v0++110nil30Marked_merge30u0