$$R = 1 - H(X)/\log|A|$$ Shannon (1948), Section 7: "The ratio of the entropy of a source to the maximum value it could have while still restricted to the same symbols will be called its relative entropy ... One minus the relative entropy is the redundancy."
Examples
Redund(c(0.5, 0.5))
#> $estimate
#> [1] 0
#>
#> $entropy
#> [1] 1
#>
#> $hmax
#> [1] 1
#>
#> $relative
#> [1] 1
#>
#> $n
#> [1] 2
#>
#> $method
#> [1] "Redundancy 1 - H/Hmax -- Shannon (1948) Sec. 7"
#>
