                   list   list_of<integer>   list_of<double>   list_of<character>  
list               "list" NA                 NA                NA                  
list_of<integer>   NA     "list_of<integer>" "list_of<double>" NA                  
list_of<double>    NA     "list_of<double>"  "list_of<double>" NA                  
list_of<character> NA     NA                 NA                "list_of<character>"
