extract player class.
add minitest and travis.
rename mathy executable.
let the difficulty decide what operations the user can choose.
inline operation parameter into method.
move difficult prompt to console so the player can choose.
pass console to game and let it set up the game.
inject each operation with the difficulty.
instantiate verification in a single location as a default parameter.
move final report to console.
extract method to lookup the operation.
extract method to play all turns.