mine

gravity=0
turtle.select(16)
  sleep(3)
while turtle.compare()~=true do
   turtle.select(1)
if turtle.compareDown() then
   turtle.digDown()
   turtle.select(3)
   turtle.placeDown()
end
if turtle.detect() then
   turtle.digUp()
   turtle.up()
   gravity=0
elseif turtle.detectDown() then
turtle.forward()
gravity=1
else
  if gravity==1 then
    turtle.down()
  else
    turtle.forward()
  end
end
turtle.select(16)
   end