The Epsilon Game
Players agree on a function f(x) and enter it. For some input value x=c (also entered by the players), a "candidate limit" value L is entered, as the alleged limit of f(x) as x approaches the value c.
Player 1 chooses a "target tolerance" epsilon to define an interval about L. The goal of Player 2 is to choose "response input distance" delta to define an interval around x=c, with the goal that all of the graph between the blue dotted lines defined by delta should lie inside the green "Goal Box".