ABSTRACT
The object of Coding Theory is the transmission of messages over noisy channels. One illustration for the claim that every message can be represented by bitstrings is the Morse code, which has been in use for telegraphy since the 1840s. Transmitter and receiver agree on the code to be used. If only one error occurs in the channel, then the received word will be in a ball of radius 1 around a codeword. Error detection is a more modest aim than error correction. The classical commercial codes use five letter groups as codewords. In modern terminology the business of representing messages by short strings is called Data Compression or Source Coding. However, commercial telegraphy codes also took the reliability of message transmission into consideration. A general rule known as the two-letter differential stipulated that any two codewords had to differ in at least two letters.
