Greek characters in normal and sans serif math mode

Question

Here's a simple demonstration program:

\documentclass[12pt]{article}
\usepackage[utf8x]{inputenc}

\DeclareMathVersion{sans}
\SetSymbolFont{letters}{sans}{OT1}{cmss}{m}{sl}

\begin{document}
\[
    x +  \alpha \beta
\]
\mathversion{sans}
\[
    x  + \alpha \beta
\]
\end{document}  

It works fine, but the sans serif math does not have correct greek characters. Adding the following lines almost fixes the problem:

\usepackage[LGR]{fontenc}
\DeclareSymbolFont{grekletters}{LGR}{cmr}{m}{sl}
\DeclareMathSymbol{\alpha}{\mathord}{grekletters}{`a}
\DeclareMathSymbol{\beta}{\mathord}{grekletters}{`b}
%...
\SetSymbolFont{grekletters}{sans}{LGR}{cmss}{m}{n}

But now the Greek characters in math mode are not the original ones. Where are the original ones?

There's a similar question: Replacing greek glyphs in math mode. It is about luatex, though.

Also, I cannot use the sansmath package because it does not support my font encoding.

Answer 1

The letters font should be a font encoded as OML, not OT1; you can use CMBright for those and for the OMS family; a decent substitute for the large symbols can be Iwona:

\SetSymbolFont{operators}   {sans}{OT1}{cmss} {m}{n}
\SetSymbolFont{letters}     {sans}{OML}{cmbrm}{m}{it}
\SetSymbolFont{symbols}     {sans}{OMS}{cmbrs}{m}{n}
\SetSymbolFont{largesymbols}{sans}{OMX}{iwona}{m}{n}