This is simply 'in', but applies `base::toupper()`

to both
arguments, first.

`find %IN% table`

- find
The element(s) to look up in the vector or matrix.

- table
The vector or matrix in which to look up the element(s).

A logical vector.

```
letters[1:4] %IN% LETTERS
#> [1] TRUE TRUE TRUE TRUE
```