In other words, to have a perfect forgery you must not know it is a forgery. If you could screen for knowing that a bill is a forgery, it would be useless to ma

In other words, to have a perfect forgery you must not know it is a forgery. If you could screen for knowing that a bill is a forgery, it would be useless to make one (since you could not spend it, since you knew it was a forgery). Bummer we can't. /s