Can God create a mountain so heavy that he cannot lift it? If he can lift it, then he couldn't have made it THAT heavy - this is a blow to his omnipotence. If he can make it that heavy that it becomes impossible for him to lift it, then he has never been omnipotent to begin with.
This is something I have just recently come across. There are some explanations found on the paradox in the net too, will have to look it up.
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