How do I import these three specific symbols from mathabx?

Question

I would like to use the symbols \smalltriangleup, \smalltriangledown and \blacktriangleup from mathabx. The problem is that if I use the mathabx package, some of the other symbols change (like \infty and \emptyset). How could I use those three specific symbols without affecting the rest of the symbols?

Answer 1

Copy the relevant lines of the style file to your preamble.

\documentclass{article}
\DeclareFontFamily{U}{mathb}{\hyphenchar\font45}
\DeclareFontShape{U}{mathb}{m}{n}{
      <5> <6> <7> <8> <9> <10> gen * mathb
      <10.95> mathb10 <12> <14.4> <17.28> <20.74> <24.88> mathb12
      }{}
\DeclareSymbolFont{mathb}{U}{mathb}{m}{n}
\DeclareFontSubstitution{U}{mathb}{m}{n}
\DeclareMathSymbol{\smalltriangleup}   {2}{mathb}{"98}
\DeclareMathSymbol{\smalltriangledown} {2}{mathb}{"99}
\DeclareMathSymbol{\blacktriangleup}   {2}{mathb}{"9C}
\begin{document}
$a\smalltriangleup b\smalltriangledown c \blacktriangleup d$
\end{document}