syntax error

im getting a syntax error on 53 here is my code


local args = {…}
local dist = tonumber(args[1])
turtle.forward()
turtle.turnRight()
turtle.forward()
turtle.select(16)
turtle.place()
turtle.back()
turtle.turnLeft()
turtle.back()

turtle.up()
for i=1,dist,1 do

turtle.select(1)
turtle.place()
turtle.turnLeft()
turtle.forward()
turtle.turnRight()
end
turtle.place()
turtle.back()
for i=1,dist,1 do
turtle.select (2)
turtle.place()
turtle.turnRight()
turtle.forward()
turtle.turnLeft()
end
turtle.place()
turtle.up()
turtle.up()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.down()
turtle.turnLeft()
turtle.turnLeft()
for i=1,dist,1 do
turtle.place()
turtle.turnRight()
turtle.forward()
turtle.turnLeft()
end
turtle.place()
turtle.down()
turtle.down()
turtle.forward()
turtle.turnLeft()
while turtle.forward() do
end
turtle,back()
for i=1,dist,1 do
turtle.select(2)
turtle.place()
turtle.back()
end
turtle.place()
turtle.turnLeft()
turtle.forward()
turtle.turnRight()
for i=1,dist,1 do
turtle.forward()
end


any help would be great

turtle,back() should be turtle.back()

thanks that fixed it