`tilde operator`

is often used to denote a statistical model, where the thing on the left of the `~`

is the response and the things on the right of the `~`

are the explanatory variables.

here is an example `fo <- y ~ x1*x2`

this line of code from this post

```
coordinates(meuse) = ~x+y
```

let's leave coordinates alone temporally.

in the case of

```
x = 1
y = 2
```

(or another more reasonable concrete example)

what is the detailed procedure of ~x+y operation?