Buscar a referência

## To cite the MASS package in publications use:
## 
##   Venables, W. N. & Ripley, B. D. (2002) Modern Applied Statistics with
##   S. Fourth Edition. Springer, New York. ISBN 0-387-95457-0
## 
## A BibTeX entry for LaTeX users is
## 
##   @Book{,
##     title = {Modern Applied Statistics with S},
##     author = {W. N. Venables and B. D. Ripley},
##     publisher = {Springer},
##     edition = {Fourth},
##     address = {New York},
##     year = {2002},
##     note = {ISBN 0-387-95457-0},
##     url = {https://www.stats.ox.ac.uk/pub/MASS4/},
##   }