Found it:

```
impl<'d> embedded_hal_1::digital::OutputPin for OutputOpenDrain<'d> {
    #[inline]
    fn set_high(&mut self) -> Result<(), Self::Error> {
        Ok(self.set_high())
    }

    #[inline]
    fn set_low(&mut self) -> Result<(), Self::Error> {
        Ok(self.set_low())
    }
}
```
But how does the compiler know, which of the identically named functions I am using. I didn't know that this is allowed.