My favorite bit of 'tax law': Decades ago I accidentally failed to file a return and ended up needing to compute some interest and penalties when I figured it

My favorite bit of 'tax law': Decades ago I accidentally failed to file a return and ended up needing to compute some interest and penalties when I figured it out a year later. When trying to determine how the computation was done exactly, I found a court case where the IRS petitioned the court to let them approximate the results of this specific computation because applying the rule exactly was too complicated for them! [I did eventually figure it out.]