clauses for the same predicate should be grouped - turbo-prolog

Question

Here I want to make a prolog implementation that will generate the list of permutations of n,n+1,...2*n-1, having the absolute difference between 2 consecutive values <=2.
Ex: for n=4 the list on which I make the permutations would be [4,5,6,7] , a valid permutation would be [5,4,6,7] and not a valid one would be [7,4,6,5] because 7-4 is 3 . The problem is that I get the following error clauses for the same predicate should be grouped. I don't understand what I did wrong..Please help me
domains
el=integer
list=el*
lista=list*
predicates
perm(list,list)
permutations(integer,list)
delete(integer,list,list)
generate(integer,lista)
create(integer,list)
create_list(integer,integer,list)
permutations_aux(integer,list)
diff(list,integer).
clauses
create(N,L):-
M = 2*N,
create_list(N,M,L).
create_list(N,M,[N|R]):-
N<M,
N1=N+1,
create_list(N1,M,R).
create_list(M,M,[]).
perm([],[]).
perm(Y,[A|X]):-
delete(A,Y,Y1),
perm(Y1,X).
delete(A,[A|X],X).
delete(A,[B|X],[B|Y]):-
delete(A,X,Y).
permutations(N,X):-
create(N,X1),
perm(X1,X).
diff(X,2).
permutations_aux(N,X):-
permutations(N,X).
diff([],_).
diff([_],_).
diff([X,Y|T],M):-
abs(Y-X) <=M,!,
diff([Y|T],M).
generate(N,R):-
findall(X,permutations_aux(N,X),R).
goal
generate(4,P),
write(P).

Answer 1

The error or warning:
Clauses for the same predicate should be grouped
Means that you have interleaved definition of different clauses. In other words, clauses for a predicate with the same name should all be defined together in a group. Such as:
foo(X) :-
some stuff
foo(Y) :-
some stuff
bar(X) :-
some stuff
bar(Y) :-
some stuff
You will get the warning/error if you do:
foo(X) :-
some stuff
bar(X) :-
some stuff
foo(Y) :-
some stuff
bar(Y) :-
some stuff
Your error is that you have a period after perm(X1,X). in your permutations clause. It should be a comma:
permutations(N,X):-
create(N,X1),
perm(X1,X). <--- Error here
diff(X,2).
permutations_aux(N,X):-
permutations(N,X).
diff([],_).
So it really thinks you have:
permutations(N,X):-
create(N,X1),
perm(X1,X).
diff(X,2).
permutations_aux(N,X):-
permutations(N,X).
diff([],_).
Which is an interleave of definitions for diff.