def check_coords(x, y)
			if 0 <= x && x < 8 && 0 <= y && y < 8
				true
			else
				fail ArgumentError, "coord (#{x},#{y}) outside of permitted range ((0..7), (0..7))"
			end
		end
def check_coords(x, y)
			if 0 <= x && x < 8 && 0 <= y && y < 8
				true
			else
				fail ArgumentError, "coord (#{x},#{y}) outside of permitted range ((0..7), (0..7))"
			end
		end
Verify supplied coords +x+ and +y+

 Raises ArgumentError if the supplied coords are invalid
 (doesn't address configured pixel)