\chapter{Greek-letter identifiers}
\label{chap:greeks}

As mentioned in chapter~\ref{chap:hello}, the sole exception to the
requirement that hansl identifiers must be plain ASCII is that they
may take the form of a single Greek letter. Here are the details.

\begin{itemize}
\item This exception applies only to names of variables \textit{other
    than series}; the names of series must always be ASCII.
\item The supported Greek characters are the 24 (unaccented) letters
  in the basic Greek alphabet, minus omicron, which is
  indistinguishable from the Latin `o'.
\item These letters may be used in lower or upper case (constituting
  distinct identifiers, as usual in hansl), except for the several
  upper-case letters which are indistinguishable in the Latin and
  Greek alphabets (`A', `B', `E', `K', `M', `N', \dots).
\item The Greek letters must be encoded in UTF-8.
\end{itemize}

In gretl's graphical interface (script editor and GUI ``console''),
the acceptable Greek letters can be entered by typing a Latin letter
while the \texttt{Alt} key is depressed. The mappings from Latin to
Greek are shown below: lower case first, then upper case.

\begin{center}
  \begin{tabular}{ccl@{\hskip 4em}ccl}
    Latin & Greek & & Latin & Greek \\[4pt]
    a & $\alpha$ & alpha & n & $\nu$ & nu \\
    b & $\beta$ & beta & p & $\pi$ & pi \\
    c & $\chi$ & chi & q & $\theta$ & theta \\
    d & $\delta$ & delta & r & $\rho$ & rho \\
    e & $\epsilon$ & epsilon & s & $\sigma$ & sigma \\
    f & $\phi$ & phi & t & $\tau$ & tau \\
    g & $\gamma$ & gamma & u & $\upsilon$ & upsilon \\
    h & $\eta$ & eta & v & $\nu$ & nu \\
    i & $\iota$ & iota & w & $\omega$ & omega \\
    j & $\psi$ & psi & x & $\xi$ & xi \\
    k & $\kappa$ & kappa & y & $\upsilon$ & upsilon \\
    l & $\lambda$ & lambda & z & $\zeta$ & zeta \\
    m & $\mu$ & mu \\
  \end{tabular}
\end{center}

\begin{center}
  \begin{tabular}{ccl}
    Latin & Greek \\[4pt]
    D & $\Delta$ & Delta \\
    F & $\Phi$ & Phi \\
    G & $\Gamma$ & Gamma \\
    J & $\Psi$ & Psi\\
    L & $\Lambda$ & Lambda \\
    P & $\Pi$ & Pi \\
    Q & $\Theta$ & Theta \\
    S & $\Sigma$ & Sigma \\
    U & $\Upsilon$ & Upsilon \\
    W & $\Omega$ & Omega \\
    X & $\Xi$  & Xi \\
    Y & $\Upsilon$ & Upsilon \\
  \end{tabular}
\end{center}

A word of advice: it's probably not a good idea to employ Greek-letter
identifiers in hansl scripts that you intend to share via the
internet, since one cannot assume that text encodings are preserved
unchanged. This warning applies in particular if you, or any of the
intended recipients of your scripts, work on MS Windows, since Windows
does not natively support UTF-8, the mandatory encoding of such
identifiers for use with gretl.
