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You probably meant Steem Power.

Here it is, directly from the white paper:
If people could freely convert in both directions then traders could take advantage of the
blockchains conversion rates by trading large volumes without changing the price. Traders
who see a massive run up in price would convert to SMD at the high price (when it is most
risky) and then convert back after the correction. The Steem protocol protects the
community from this kind of abuse by only allowing people to convert from SMD to STEEM
and not the other way around.
The blockchain decides how and when to create SMD and who should get it. This keeps the
rate of SMD creation stable and removes most avenues of abuse.

yes. I believe the key word in this is convert. You can buy between SD and Steem. We have an internal market to do that.

What is the difference between convert and "buy." Maybe they just evolved the rules since they wrote the paper...

what I can see is that if I want to convert it says something about 7 days. I had to do a sample, because I want to take my SD and buy STEEM. I bought some STEEM, the turned right back around and sold it for SD. I can send the STEEM to my exchange, and vice versa.

So, I really don't know...lol