suppress odd icons for documents and folders;

support for modified tree cell renderer;

clarified signature: avoid implicit functionality;

re-use Output_Area;

re-use Output_Area;

re-use Output_Area;

re-use Output_Area with search results;

re-use Output_Area with search results;

more thorough init;

clarified signature: prefer defaults for Output_Dockable (and its variants);

unused;

tuned output: formatting is pointless for proportional font;

clarified Tree_View.init_model: more uniform;

more robust update;

handle tree selection;

Output_Dockable: show search results as tree view;

clarified modules;

clarified signature;

clarified signature;

clarified signature and modules: without GUI change yet;

more operations, to support search within output panel;

tuned;

Introduced the function some_elem for grabbing an element from a non-empty set, and simplified the theorem the_elem_image_unique

Patch by Stepan Holub, plus tweaks

patch to vector_matrix_mult by Alexander Pach

try0: cleaned up output;

try0: insert extra facts into state instead of goal, since some methods (e.g. metis) won't work otherwise;

avoid informatik.tu-muenchen.de domain: soon to be discontinued;