Pretty printing parse trees

I now want to introduce some built-in predicates for writing output to the screen.

write/1 takes a Prolog term as argument and prints this term onto the screen. For example:
```
?- write(cook(snape,potion)).
cook(snape, potion)

Yes
    
```
tab/1 takes a number as argument and prints as many spaces onto the screen. For example:
```
?- write(a),write(b).
ab

Yes
?- write(a),tab(5),write(b).
a     b

Yes
    
```
nl prints a newline onto the screen. For example:
```
?- write(a),nl,write(b).
a
b

Yes
```

Now, use these predicates to define a predicate pptree/1 that takes a complex term representing a tree, such as s(np(det(the),n(bride)),vp(v(kills),np(det(a),n(man)))), as its argument and prints a nicer and more readable output for this tree to the screen. For example, something like this

s(
  np(
     det(the)
     n(bride))
  vp(
    v(kills)
    np(
      det(a)
      n(man))))

Hint: You will need the built in predicates functor and arg for this. (See this exercise of day 1.) The built in predicate =.. might also be useful. =.. turns a complex term with n arguments into a list of n+1 elements. The first element of the list is the functor of the complex term and the other n elements are the arguments of the complex term.

?- f(a,b,c(d)) =.. L.
L = [f, a, b, c(d)] ;
no

Hint

Back to the practical session of day 5.