You have your thinking backwards because you're ignoring the need for a counterparty. In order for your sale to happen the market must first find a buyer to match it with (otherwise how could you trade?). There's no need to mathematically prove there isn't some other buyer as the whole point is to match the two.
Limit orders at the same price are filled in FIFO order, and it can be the case that that some limit orders fill while others do not simply because someone was only willing to buy 100 shares at that price and there were 200 available for sale - some sales won't happen.
Limit orders at the same price are filled in FIFO order, and it can be the case that that some limit orders fill while others do not simply because someone was only willing to buy 100 shares at that price and there were 200 available for sale - some sales won't happen.