Lua排序。sort排序后的怪异顺序

crdsClear={{y=56,x=50,symbolName=3,},
{y=56,x=29,symbolName=2,},
{y=56,x=99,symbolName=2,},
{y=56,x=9,symbolName=5,},
{y=56,x=69,symbolName=5,},
{y=56,x=19,symbolName=4,},
{y=56,x=59,symbolName=4,},
{y=56,x=89,symbolName=4,},
{y=56,x=40,symbolName=7,},
{y=56,x=80,symbolName=6,},}

tmp2={}
ywf = 1
table.sort(crdsClear,
    function(a,b)
        tmp2[ywf]=""
        for i=1, #crdsClear, 1 do tmp2[ywf] = tmp2[ywf].."\t"..crdsClear[i].x     end
        ywf = ywf + 1
        if  a.x <= b.x then print(a.x.." <= "..b.x.." true") else print(a.x.." <= "..b.x.." false") end
        return a.x <= b.x --  a.y <= b.y and
    end
)

-- 创建字符串
order=""
print(#crdsClear)
result = {[1]=""}
for i=1, #crdsClear, 1 do
    order = order..crdsClear[i].x.." "
    result[1] = result[1].. crdsClear[i].symbolName
end
print(order)
print(result[1])

sort排序后我有一个.x顺序：

9 19 59 29 40 50 69 80 89 99

和字符串：

5442735642

为什么我有不正确的顺序？

如果我改变：

return a.x <= b.x

to:

return a.x < b.x

然后正确地排序。