lib/texinputs/isabellesym.sty

 \newcommand{\isasymbind}{\isamath{\mathbin{>\!\!\!>\mkern-6.7mu=}}}
 \newcommand{\isasymthen}{\isamath{\mathbin{>\!\!\!>}}}
 \newcommand{\isasymsome}{\isamath{\epsilon\,}}
 \newcommand{\isasymopen}{\isatext{\raise.3ex\hbox{$\scriptscriptstyle\langle$}}}
 \newcommand{\isasymclose}{\isatext{\raise.3ex\hbox{$\scriptscriptstyle\rangle$}}}
+\newcommand{\isasymnewline}{\isatext{\fbox{$\hookleftarrow$}}}