Homework 3.

==============

1. Write a predicate that accepts a list and succeeds if that list has exactly three elements.

=============

2. Write a predicate that accepts a list and generates from it a similar
list with the first two elements swapped.

It should work like this:

?-swap_first_two([a,b,c,d], [b,a,c,d]).

Yes

?-swap_first_two([a,b,c,d], X).

X= [b,a,c,d];

No

?-swap_first_two(X, [b,a,c,d]).

X=[a,b,c,d];

No

?-swap_first_two([a,b,c,d], [b,a,d,c]).

No

?-swap_first_two([a,b,c,d], [X,Y,c,d]).

X=b
Y=a;

No

=================================

3. Define the relation reverse_list(List, Reversed_List) that
reverses lists, e.g.:

?- reverse_list([a,b,c,d],[d,c,b,a]).

yes

?- reverse_list([a,b,c,d],X).

X=[d,c,b,a];

No

=================================

4. Define the predicate palindrome(List) that recognizes palindromes.

A list is a palindrome if it reads the same in the forward and in
the backward direction. For example:

?- palindrome([m,a,d,a,m]).

yes

?- palindrome([s,i,r]).

No

=================================

5. Define the relation shift(List1, List2) so that List2 is List1
"shifted rotationally" by one element to the left. For example,

?- shift([1,2,3,4,5], L1), shift(L1,L2).

L1=[2,3,4,5,1]
L2=[3,4,5,1,2];

No

================================

6. Define the relation maximum(List,Integer) that succeeds if Integer
is the maximal element of the list of integers List. Example,

?- maximum([1,2,3,4,2,-1,4],Max).

Max=4;

No

?- maximum([],Max).

No