" Create the mapping which will toggle the cheatsheet
nnoremap <F1> :call Cheatsheet()<CR>

function! Cheatsheet()
    " Save the z register
    let save_z = getreg('z')

    " Get the list of buffers in the z register
    redir @z
        silent filter /cheatsheet/ ls
    redir END

    " Get the result in a variable and restore the register
    let buff = getreg('z')
    call setreg('z', save_z)

    " The results has several lines, make it only one
    let buff = substitute(buff, 'n', '', 'g')

    " Get the status (hiden 'h' or not 'a') of the buffer
    let status = buff[match(buff, '[ah]')]

    " If the buffer is not hidden delete it, that will close the split
    if status == "a"
        let buffnumber = substitute(buff, '^s*', '', '')[0]
        execute "bdelete " . buffnumber
    " Else open a split
    else
        vsplit ~/.cheatsheet
    endif
endfunction