+ if read1 == 0 && read2 == 0 then begin
+ let l1 = Queue.length ctx1.events in
+ let l2 = Queue.length ctx2.events in
+ if l1 > l2 then let _, p1 = Queue.pop ctx1.events in raise (Diff p1)
+ else if l2 > l1 then let _, p2 = Queue.pop ctx2.events in raise (Diff p2)
+ else common_prefix ctx1 ctx2 l1
+ end else begin