In the US, is it in principle allowed to compute a capital gain/loss by reversing the order of purchase and sale? Here is an example: Assume, on day 1 you buy 1 unit of an asset for 100 dollars. 60 days later, you sell that 1 units of that asset for 200 dollars. 60 days later yet, you buy 1 unit of that asset again for 300 dollars. It seems you would have made a short term capital gain of 100 dollars, and the basis for the asset you hold is 300. Is it legal to claim a short term loss of 100 (allocating the purchase for 300 to the sale), and assigning a basis of 100 to the asset that is still held?
EDIT: It seems "obvious" the answer is no, but can we point to any authoritative reference to confirm that? The answer is not obvious because in a short sale of an asset a purchase is matched with an earlier sale by definition.