gap> # test method-not-found traceback rendering while preserving helper access
gap> f := a -> IsDiagonalMat(a);;
gap> f(());
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `IsDiagonalMatrix' on 1 arguments
Stack trace:
*[1] IsDiagonalMat( a )
   @ *stdin*:3
<function "f">( <arguments> )
 called from read-eval loop at *stdin*:4
type 'quit;' to quit to outer loop
brk> ShowMethods(1);
#I  Searching Method for IsDiagonalMatrix with 1 argument:
#I  Total: 3 entries
brk> Where(5);
*[1] IsDiagonalMat( a )
   @ *stdin*:3
<function "f">( <arguments> )
 called from read-eval loop at *errin*:2
brk> quit;
gap> QUIT;
