Real blockchains do have a blockheader.prevHash field to indicate that the previous block is the one satisfying HASH(prevheader) == blockheader.prevHash T

Real blockchains do have a blockheader.prevHash field to indicate that the previous block is the one satisfying HASH(prevheader) == blockheader.prevHash This one actually adds a blockheader.hash field and instead compares prevheader.hash == blockheader.prevHash Naive indeed:-)