Base R has had the function isTRUE() for many years, and I had wished for a
few years that there were an isFALSE(), too. I had used identical(x, FALSE)
many times before I added it to the first version of the xfun package as the
function isFALSE(). The xfun package was first released to CRAN on
2018-01-22.
Three months later (2018-04-23), R 3.5.0 was released, which included a function
named isFALSE() in the base package. Apparently another mind was thinking like
me (which turned out to be …