We don't stop algos from competing with one another, that said it is illegal for us as a firm to be both sides of a trade, that is we are buying/selling to ours

We don't stop algos from competing with one another, that said it is illegal for us as a firm to be both sides of a trade, that is we are buying/selling to ourselves in what is referred to as a wash trade. This can happen if algo A is buying Microsoft at the same time that algo B is selling Microsoft. We do prevent this by using a fairly standard component called an internalizer. Almost all of our orders go through such an internalizer and if it sees that two orders are matching one another, the internalizer will perform that match directly instead of having it go to the market. This happens quite frequently in fact, and it's good to be able to catch it beforehand, avoids paying fees, having any kind of market impact, as well as obviously complying with regulations.