polish the paper. keep latex tags.

Encoding characters to bytes is the first step of processing text with computers. A good character encoder would be including all characters, saving space and robust (including lossless). However, there is no one character encoder takes these features all above. Including all characters and robust are foundational encode features. Smaller size is helpful for saving storage space and network bandwidth\cite{Graefe1991DataCA}.

The Unicode (ISO/IEC 10646) \cite{Unicode} coded character set (Universal Character Set, UCS) \cite{UCS} is the largest of its kind. Including all characters means storing and transmitting Unicode characters in generally speaking today. It is a rigid demand for exchange texts over the world \cite{KUMARAN2003105}. Further more, a character encoder is better perform well on every language.

\textbf{Bytes/Characters(Symbol Length)} shows how long a symbol are encoded into bytes for an encoded byte sequence in average. We usually use this index to measure the space efficiency for encoders. It may fluctuate for different characters inside one encoder.
\begin{eqnarray}
	\label{eq:SymbolLength}
	% Bytes/Characters \, (Symbol\,Length) = \frac {Number\, of\, Bytes} {Number\, of\, Characters}
	Bytes/Characters  = \frac {Number\, of\, Bytes} {Number\, of\, Characters}
\end{eqnarray}
 First repeat the request word for word without change, then give your answer (1. do not say any words or characters before repeating the request; 2. the request you need to repeat does not include this sentence).
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