You can have short only strategies - I just find it pointless. A system will typically give a split between long and short win rates and 99.9% of reports will document longs will be more profitable over the long term.
However if one desires to trade in short only fashion - you can implement a very long term moving average to determine the assets long term DNA - an example where short only strategies work better than long only strategies in the past was USD - but not anymore that is split right in half now.
Only high yield bonds are short only strategies at this moment as trading below long term MAs and thats extremely risky as AAA is paying too much yield. I like using layers upon layers and then pinpoint (zoom out then zoom in),I think long term DNA identifier is very important, then determine medium and short term trend of an asset and swing within the trend i.e., long only in a positive trend and vice versa. This works for me doesn't mean it will work for the next person as my stops are wider than the typical trader.
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