We ran testcase1 (two enqueuers and 1 dequeuer) and get result1.txt, then we ran
testcase2 (1 enqueuers and 2 dequeuers) based on result1.txt and got
result2.txt. We can't infer the wildcard(4) to be acquire because we can't reach
"that case"!!! 
See
http://stackoverflow.com/questions/3873689/lock-free-queue-algorithm-repeated-reads-for-consistency