So how does the system prevent this kind of fraud? Each *block* contains a reference to the previous *block (see Fig. 6)*, and that reference is part of the mathematical problem that needs to be solved in order to spread the following *block* to the network. So it’s extremely hard to pre-compute a series of blocks due to the high number of random guesses needed to solve a *block* and place it on the blockchain. Mary is in a race against the rest of the network to solve the math problem that allows her to place the next block on the chain. And even if she solves it before anyone else, it’s very unlikely she could solve 2, 3 or more blocks in a row, since every time she is competing against the whole network. So, could Mary use a super fast computer to generate enough random guesses to compete with the whol…