These are important documents
{cite}friedman_regularization_2010,
{cite}friedman_additive_2000-1,
{cite}friedman_stochastic_2002, and
{cite}chen_xgboost:_2016
All together:
{cite}friedman_regularization_2010,friedman_additive_2000-1,friedman_stochastic_2002,chen_xgboost:_2016
:style: unsrt