anchor.diff:    check_illegal_filename_chars(ImageFile),
     %% all good so return string
     ImageFile;
  -check_image_file(ImageFile) ->
  +check_image_file(_ImageFile) ->
     erlang:error(imageFile_is_not_binary_nor_list).
   
   check_illegal_filename_chars( [] ) ->
  
positive.code:   %% valid so return atom
    julian;
  %% add other valid fractal algorithms here as they are created
  check_fractal_alg(FractalAlg) ->
    erlang:error(this_fractal_algorithm_not_implemented).
  
  %% get and validate image file name
  
negative.code:         ->
    %% passed checks so return Height
    Height;
  check_height(_Height) ->
    %% failed checks so fail with atom indicating issue
    erlang:error(height_must_be_integer_1_to_9999).
  
  