# [R], 35 bytes

<!-- language-all: lang-r -->

    function(W)any(seq(u<-unique(W))-u)

[Try it online!][TIO-kyngvshr]

[R]: https://www.r-project.org/
[TIO-kyngvshr]: https://tio.run/##dY@7DsIwDEV3PqNTMmRFIJUPYEdizpOGh0PSGGh/PgTRpZIzWJauj@XjVNyhOASdfQB25hImNtrIsBcIPqKtGRfIi2OY3e4UjpBZJzsu9lu@WYeSjpVUNK60bizoWmbpNKKNdZfBX2/3B4RnTGPG1/szzcOCr3lagLyuZENKGZpvmTTEU33K/Np/XL4 "R – Try It Online"

Takes input as a vector of integers from `1` to `26`. Outputs `FALSE` for truthy and `TRUE` for falsey.