theorem like environment are conflicted with template using cls file that already define it. #1001
Description
This comes from test in rstudio/rticles#288
lipics-v2019.cls already defines theorem like environment. When using this articles with pdf_book to get the \@ref syntax, this does not work because bookdown will add in the tex template theorem like environment, but it conflicts with the one already defined by the the cls file.
Try
bookdown::pdf_book:
base_format: rticles::lipics_article()with LIPICs template from rticles