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#### Posting Guidelines

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(OP)
Hello... I really need help with these examples... Thank You...

1) sum (List, X)

Predicate stored in the variable X total value of all elements of list List.

2) double (List, ListList)

Predicate stored in the variable ListList list where each list element List occurs twice in a row.

What did you try ?

(OP)
I have this for first example and I don´t know if is it right...

sum([],0).
sum([H | T], S) :-
integer(H),
sum(T, S1),
S is S1 + H.

It looks correct.

(OP)
Fine... That´s great... Thank You... But I don´t know, how to do second example... I really need help... I have a exam on friday...

(OP)
Is that correct?

?- dupli([a,b,c],2,X).
X = [a,a,b,b,c,c,]

(OP)
Or this is correct? Pleas reply...

double([],[]).
double([H|T],[H,H|Y]) :- double(T,Y).

#### CODE

double([],[]).
double([H|T],[H,H|Y]) :- double(T,Y).
This is correct.

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