49     using reference = value_type&;  variable
110     reference operator*() const {
122     reference operator[]( difference_type k ) const {
240         using reference = T&;  variable
267     using reference = value_type&;  variable
421     reference operator[]( size_type index ) {
428     reference at( size_type index ) {  in at()
445     reference front() {  in front()
453     reference back() {  in back()
741     reference internal_subscript( size_type index ) {  in internal_subscript()
750     reference internal_subscript_with_exceptions( size_type index ) {  in internal_subscript_with_exceptions()