* src/ltlast/bunop.hh (is_bunop, is_Star): New functions.
* src/ltlast/multop.hh (is_And, is_Or): Fix constness.
(is_Concat, is_Fusion): New functions.
* src/ltlast/unop.hh (is_unop, is_X, is_F, is_G, is_GF, is_FG):
Fix constness.
(is_Not): New function.
* src/ltlvisit/tostring.cc (strip_star_not, match_goto,
emit_bunop_child, resugar_concat): New methods.
(visit(bunop)): Rewrite without calling format().  Detect the
[->i..j] pattern.
(visit(multop)): Call resugar_concat to detect [=i..j] patterns.