it is interesting., page-11

If you look at the trading packages you will see they are algo trades. You can tell by the size of the trades and the timings. If you have a trading platform like ETrade or Nabtrade, take a look and you will see many same size parcels being exchanged in the same time frame, but broken into separate transactions. Another algo trading sign is that they usually are not in nice round numbers. The closing action today wasn't anywhere near round numbers.

If it were day traders one would see transactions spread over different time frames and in different parcel sizes. The trades were definitely done by an algorithmic program (bot).

There are many money managers that run Long/Short funds. Sometimes they can have the same stock held as both a Long and a Short. That is one way they can buy from themselves even though the accounting might be under separate identifiers/accounts/structures. It is a bit like transfer pricing in corporate accounting, if you know what that means. It is like balancing the books to best effect within the same Group.

Cheers