Thank you.
After fixing that issue, I get the following warning. Looks like there is something fundamently wrong with the mathematical gem ...
current directory: /home/lmeier/.gem/ruby/2.3.0/gems/mathematical-1.6.7/ext/mathematical
make "DESTDIR="
compiling cairo_callbacks.c
compiling mathematical.c
In file included from ./mathematical.h:14:0,
from mathematical.c:23:
/usr/include/glib-2.0/glib/gi18n.h:26:0: Warnung: »_« redefiniert
#define _(String) gettext (String)
In file included from /usr/include/ruby-2.3.0/ruby/ruby.h:36:0,
from /usr/include/ruby-2.3.0/ruby.h:33,
from ./mathematical.h:4,
from mathematical.c:23:
/usr/include/ruby-2.3.0/ruby/defines.h:83:0: Anmerkung: dies ist die Stelle der vorherigen Definition
# define _(args) args
mathematical.c: In Funktion »process«:
mathematical.c:104:5: Warnung: Implizite Deklaration der Funktion »mtex2MML_free_string« [-Wimplicit-function-declaration]
mtex2MML_free_string(mathml);
^~~~~~~~~~~~~~~~~~~~
mathematical.c:138:77: Warnung: Übergabe des Arguments 2 von »cairo_svg_surface_create_for_stream« erzeugt Zeiger von Ganzzahl ohne Typkonvertierung [-Wint-conversion]
surface = cairo_svg_surface_create_for_stream (cairoSvgSurfaceCallback, self, width_pt, height_pt);