[
 (program) {
  (function_definition) {
   (decl_specifiers) {
    vector
   }
   (operator_overload_declaration) {
    &
    operator=
   }
   (formal_args_list) {
    (
    (arg_list) {
     (arg) {
      (decl_specifiers) {
       vector
      }
      (lvalue) {
       &
       a
      }
     }
     ,
     (arg) {
      (decl_specifiers) {
       vector
      }
      (abstract_declarator) {
       &
      }
     }
    }
    )
   }
   (function_body) {
    {
    (stmt_list) {
     (return_statement) {
      return
      (expr_dereference) {
       *
       this
      }
      ;
     }
    }
    }
   }
  }
 }
]