global a; /// \sleftarrow{\normalfont \verb+a+ is now a global variable, its default value is \verb+[]+}
isglobal(a)       /// \sleftarrow{\normalfont just checks  \ldots }
function f(); global('a'); a=int(10*rand(1,4)); endfunction 
f()  /// \sleftarrow{\normalfont calling \verb+f+, which contains a global declaration of \verb+a+}
a         /// \sleftarrow{\normalfont calling \verb+f+ has changed \verb+a+}