::: {.cell hash='02_R_introduction_cache/revealjs/unnamed-chunk-36_618480e41dc61dae49c42be1ccc8991e'}

```{.r .cell-code}
b <- "this variable has a value"
is.na(b)
```

::: {.cell-output .cell-output-stdout}
```
[1] FALSE
```
:::
:::