I want to print a term with variable letters like this:

```
?- print_term(f(X,Y,X), []).
f(A,_,A)
```

I want to do the similar thing with `format/2`

or `3`

and I cannot find correct options for it.

```
?- format('~W', [f(X,Y,X), [numbervars(false)]]).
f(_12036,_12038,_12036)
?- format('~W', [f(X,Y,X), [numbervars(true)]]).
f(_12036,_12038,_12036)
?- format('~W', [f(X,Y,X), []]).
f(_12036,_12038,_12036)
```

I am using swipl 8.0.3