I can't get this to work

[Dignity]

[lua]
parent=script.Parent

amount= Vec2D(1,1)
mx=Vec2D(5,5)
mn=Vec2D(0,0)
time=0.1

type="rise"

function rise()
parent.Size = parent.Size:add(amount)
end

function lower()
parent.Size = parent.Sizeub(amount)
end

function loop()
print(type)
if (type=="rise") and (parent.Size<=mx) then
type="lower"
elseif (type=="rise") then
rise()
elseif (type=="lower") and (parent.Size>=mn) then
type="rise"
elseif (type=="lower") then
lowerTide()
end end

while true do
sleep(time)
loop()
end
[/lua]

The error says "Script:20 _le is not defined for operand."
wut?

---

EDIT: Line 20 is "if (type=="rise") and (parent.Size<=mx) then"