A robot is in a mine and has the goal of reaching a location that
contains gold. The mine is organized as a grid with each cell either
begin hard or soft rock. There is a special location where the robot
can either pickup an endlesssupply of bombs or pickup a laser cannon.
The laser cannon can shoot through both hard and soft rock, whereas the
bomb can only penetrate soft rock. However, the laser cannon also will
destroy the gold if used to uncover the gold location. The bomb will
not destroy the gold. The problem difficulty is scaled by increasing
the size of the grid.

This domain has a simple optimal strategy:
1) get the laser cannon,
2) shoot through the rock until reaching a cell bordering the gold.
3) go and get a bomb.
4) blast away the rock at the gold location.
5) pickup the gold.
