If a conclusion can be reached in an obviously fallacious way, then the conclusion is incorrectly declared wrong.
"Take the division 64/16. Now, canceling a 6 on top and a six on the bottom, we get that 64/16 = 4/1 = 4."
"Wait a second! You can't just cancel the six!"
"Oh, so you're telling us 64/16 is not equal to 4, are you?"
In this case, an absurd argument leads to a normal conclusion. Note that this is different from Reductio Ad Absurdum, where your opponent's argument can lead to an absurd conclusion: 60/66 = 0/6 = 0 (after cancelling those pesky 6's).
See original on c2.com