First appearing in the 1963 issue of Analog Science Fact & Fiction, this story may have inspired the "holodeck" concept.

Imagine a mechanism that would end all wars and bloodshed. A machine that can create a virtual world where conflicts seem to be fought but where nobody dies. Dr. Leo's Dueling Machine is just that. When a warrior from the Kerak empire begins to win every time and finds a way to circumvent the machine and actually kill his opponents, the results are devastating and may lead to actual, not virtual war. Dr. Leo and his assistant have to work quickly to discover how this happens to save lives, planets and preserve the peace.