added generation of induction rules

simplify some proofs

restrict perspective to actual buffer_range, to avoid spurious edits due to faulty last_exec_offset (NB: jEdit screenlines may be silently extended by trailing newline);

tuned signature;

dynamic exec state lookup for implicit position information (e.g. 'definition' without binding);

some support for hyperlinks between different buffers; tuned signature;

tuned colors -- more distance between outdated_color and quoted_color;