I do think God is even able to make "two hills without a valley between them", without them becoming just one hill. I don't know what that would be like, but I do know for God everything is possible. He can do miracles, which defy any physical law or any logic. I think if we try to understand God from our limited mind we end up reducing him and thinking he is not so great, but that is just because our own limitations. We can't logically explain how God is one but at the same time is Father and Son, but they both are one and the same. Not because we can't explain it means is false. it only means that is beyond our knowledge.
As for the equation, I would suggest giving numerical values to the variables X and Y. If according to the parameters X is the biggest thing possible I could only attribute to X an Infinite value. Y would be anything that is not God and can have any value. Let's say Y is 6
Infinite + 6 = Infinite
You can try giving Y any value and the result will be the same. God is the greatest, nothing can ad or reduce any value to Him
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