The Incompleat Enchanter

The Mathematics of Magic—it was the greatest discovery ever. Or so thought Professor Harold Shea. With the proper equations he could instantly transport himself and his friend Reed Chalmers back—or sideways—in time to all the wondrous lands of ancient myth and legend.

But slips in time were a hazard. and Shea's magic didn't always work quite as he expected. A dragon spell might yield a hundred dragons—or, even worse, one-tenth of a dragon. And the various imaginary lands he travelled to held countless dangers that even Shea's equations couldn't predict...