The equals sign is missing

Question

When I use the fonts fourier and iwona at the same time, the equals sign = does not appear. For example, the source

\documentclass{article} 
\usepackage{fourier}
\usepackage[math]{iwona}
\begin{document}
$A=B$
\end{document}

produces

A B

Question: How can I fix this problem?

(*) I want to use iwona and to replace fonts for \mathbb with ones of fourier.

Remarks:

1. If I use the package fourier first, then = appears as usual. But all of the fonts are replaced by fourier fonts, so this is not the solution which I want.

2. The following error could relate to the problem.

   LaTeX Font Warning: Font shape OT1/iwonam/m/n' undefined (Font)
usingOT1/cmr/m/n' instead on input line 5.

   LaTeX Font Warning: Some font shapes were not available, defaults substituted.

3. If I use only iwona then the equals sign appears.
4. If there is a way to satisfy (*), please let me know.

Answer 1

You can load only the \mathbb alphabet from fourier:

\DeclareFontFamily{U}{futm}{}
\DeclareFontShape{U}{futm}{m}{n}{
  <-> fourier-bb % changed from .92 to 1
  }{}
\DeclareMathAlphabet{\mathbb}{U}{futm}{m}{n}

Note that I've also changed the magnification from .92 to 1 to match iwona sizes.

MWE:

\documentclass{article}
\usepackage[math]{iwona}

\DeclareFontFamily{U}{futm}{}
\DeclareFontShape{U}{futm}{m}{n}{
  <-> fourier-bb % changed from .92 to 1
  }{}
\DeclareMathAlphabet{\mathbb}{U}{futm}{m}{n}

\begin{document}
$A(x)=B(x),\quad x\in\mathbb{R}$ 
\end{document} 

Output: