why can't I type \rf to start R in vim after install the Vim-R-plugin?

Question

I install the vim-r-plugin and at the last step followed this:

Start Vim again and edit an R script. Type <LocalLeader>rf to start R and run the command below to get help configuring ~/.Rprofile, ~/.vimrc, ~/.tmux.conf, and ~/.bashrc (the <LocalLeader> is \ by default).

however, at the normal mode nowhere I can type in "\rf". I typed in ':\rf' but that's totally wrong with this message"E10: \ should be followed by /,? or &". Does anyone know what's the reason?

Answer 1

you must type \rf quickly, even hold pressing \ while r then f keys.