prolog - I am having problems getting a list of lists into a single list

Question

I am writing a solution to working out distances between numbers in a list using recursion, but have been struggling with getting the intended output. I am trying to get a list of lists into a single list, but attempts at using flatten and append/2 aren't working. I have tried for hours, and keep going around in circles, can someone tell me what i'm doing wrong please?

:- use_module(library(clpfd)).

difference([],_,[]).
differwnce([L|Ls],X,[DST|Ds]) :-
   DST #= abs(X - L),
   difference(Ls,X,Ds).

differences[],[]).
differences([L|Ls], [DST|Tail]) :-
   difference(Ls,X,DST),
   differences(Ls, Tail).

Here is the intended input and output:-

?- differences([1,2,4,9],Ds).
Ds = [1,3,8,2,7,5].

Current Output:

Ds = [[1,3,8],[2,7],[5],[]].

Answer 1

seq([]) --> [].
seq([E|Es]) --> [E], seq(Es).

seqq([]) --> [].
seqq([Es|Ess]) -->
  seq(Es),
  seqq(Ess).

?- phrase(seqq([[1,3,8],[2,7],[5],[]]), Es).
Es = [1,3,8,2,7,5].

?- dif(A,B), phrase(seqq([[A|_]|_]), [B|_]).
false.