
%Numbering of environments with a fractional environment number, see
% https://tex.stackexchange.com/questions/598076/how-to-have-a-fractional-environment-number/598080?noredirect=1#comment1499689_598080
%However, for a reason i don't understand the posted answer does not work for me, but i had to replace theorem with definition in the definition of the gag environment (so apparently, i have to do this for each environment separately). It seems that the definitions of this document do use \thedefinition and not \thetheorem, although by default this is not the case.
\newcounter{gag}
\makeatletter
\newenvironment{gag}[1]{%
  \let\savedthedefinition\thedefinition
  \thm@headfont{\bfseries\boldmath}%
  \stepcounter{gag}%
  \renewcommand{\thedefinition}{\savedthedefinition#1}%
  \renewcommand{\theHdefinition}{gag\thegag}%
  \addtocounter{definition}{-1}\ignorespaces
}{\ignorespacesafterend}
\makeatother
