p213fig05.23 A category, symbol, or other highly compressed representation cannot determine whether an error has occurred.<BR>||  Compression vs error correction. past vs present.  Where is the knowledge than an error was made? Not at F2! The compressed code cannot tell the difference! X2 is at F1 when (green right triangle GRT) is at F2 defines the error.  There is a mismatch between X1 and X2 at F1.  How does the system know this?