Title says it all, got the idea from this old answer on stack exchange
The user suggests that it is possible to train yourself to need less sleep.
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The answer that you are referring to is mistaken about biphasic/polyphasic sleep. It claims:
It is possible to train the human body into needing much less sleep.
However, nowhere does the first link provided for evidence claim that biphasic/polyphasic sleep makes the body need less sleep. The claim is that it's possible to better recover in less time in order to maintain performance when undergoing sleep deprivation, which is not the same thing at all as needing less.
The closing lines of the last link provided for evidence actually make that clear:
"… there is no denying the effects of sleep deprivation. And training the body to sleep less is not a viable option." Nothing matches a good night's sleep.