From Tcl 8.5, list non-inclusion [expr] operator. E.g. if {$el ni $list} ... Opposite of [in]. - [rs] 2007-04-26 set el Mon set list [list Mon Tue Wed Thu Fri Sat Sun] if {$el ni $list} { puts "Invalid day abbreviation" } else { puts "Valid day abbreviation" } ---- [Category Command] a subcommand of expr