Mining turtle

i=55
j=0
function inv()
  a = 1
  for a=1,9
  do
    turtle.getItemCount(a)
    a = a+1
    if turtle.getItemCount(a) >=1
    then return true
    else return false
  end
end
while i > 0 do

  turtle.digDown()
  turtle.dig()
  turtle.turnLeft()
  turtle.dig()
  turtle.turnRight()
  turtle.dig()
  turtle.turnRight()
  turtle.forward()
  turtle.turnLeft()
  turtle.turnLeft()
  i = i-1
end
while i = 0 do
  turtle.turnLeft()
  turtle.dig()
  turtle.forward()
  turtle.digUp()
  turtle.turnRight()
  turtle.dig()
  turtle.forward()
  turtle.digUp()
  turtle.turnLeft()
  turtle.forward()
  turtle.turnRight()
  j = j+1
    if inv() = true
    then
    turtle.back(j)
    turtle.up(55)
    sleep(180)
    turtle.down(55)
    turtle.forward(j)
    end
  end
end
end