function Down()
	if turtle.detectDown() then
		turtle.digDown();
	end
	turtle.down();
end

function Up()
	if turtle.detectUp() then
		turtle.digUp();
	end
	turtle.up();
end

function Forward()
	if turtle.detect() then
		turtle.dig();
	end
	turtle.forward();
end

local exvac = true;

function Begin()
	turtle.refuel();
	turtle.turnLeft();

	for x = 1, 16, 1 do

		for i = 1, 16, 1 do
			Forward();
		end

		if exvac then
			turtle.turnRight(); Forward(); turtle.turnRight();
		else
			turtle.turnLeft(); Forward(); turtle.turnLeft();
		end
		exvac = not exvac;

	end


	--[[ return to position ]]
	turtle.turnLeft();
	for i=1, 16, 1 do
		turtle.forward();
	end
	turtle.turnLeft(); turtle.turnLeft();
	Up();
	Wait();
end

function Wait()
	while true do
		local event = os.pullEvent("redstone");
		Up();
		Begin();
	end

end

while true do
	local event = os.pullEvent("redstone");
	Begin();
end