I found an interesting problem on https://www.codewars.com/kata/59b2883c5e2308b54d000013:
An onion array is an array that satisfies the following condition for all values of `j` and `k`:

If all of the following are `true`:

* `j >= 0`
* `k >= 0`
* `j + k = array.length - 1`
* `j != k`
  
then:

* `a[j] + a[k] <= 10`

### Examples:

```
[1, 2, 19, 4, 5]   =>  true  (as 1+5 <= 10 and 2+4 <= 10)
[1, 2, 19, 4, 10]  =>  false (as 1+10 > 10)
```

Write a function named `isOnionArray`/`IsOnionArray`/`is_onion_array()` that returns `true` if its argument is an onion array and returns `false` if it is not.

~~~if:php
Your solution should at least be moderately efficient.  Make sure you don't do any unnecessary looping ;)
~~~

I tried it in Python, but could not do it. Can you solve it?
def is_onion_array(a):
    for j in range(len(a)//2):
        if a[j] + a[-j-1] > 10:
            return False
    return True