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# Prolog Help Various Rules

## Prolog Help Various Rules

(OP)
Hello all! I really need some help of yours :D

I've got all these rules:

Returns all the vowels on a list

#### CODE --> Prolog

extractvowels([], []).
extractvowels([H|T], R) :- consonant(H), extractvowels(T, R).
extractvowels([H|T],[H|R]) :- \+ consonant(H), extractvowels(T, R). 

Flattens a list:

#### CODE --> Prolog

flatten([],[]).
flatten([A|L],[A|L1]) :- xatom(A), flatten(L,L1).
flatten([A|L],R) :- flatten(A,A1), flatten(L,L1), append(A1,L1,R).

xatom(A) :- atom(A).
xatom(A) :- number(A). 

Returns true or false:

#### CODE --> Prolog

member(X, [X|_]).
member(X, [_|Tail]) :- member(X, Tail). 

How can I type

#### CODE --> Prolog

extractvowels([s,a,r,a],X).
And get as result this

#### CODE --> Prolog

X = [a].
?

How can I join the rule

#### CODE -->

flatten
with the

#### CODE -->

extractvalues
?

And how can I create a rule that is able to remove the duplicates ?

PS: I can't use any of the built-in predicates :(

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