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% generated: 17 November 1989
% option(s):
%
% serialise
%
% David H. D. Warren
% Copyright: Public domain
%
% itemize (pick a "serial number" for each
% unique integer in) a list of 25 integers
top:-serialise.
serialise :- serialise(`ABLE WAS I ERE I SAW ELBA`,_).
serialise(L,R) :-
pairlists(L,R,A),
arrange(A,T),
numbered(T,1,_).
pairlists([X|L],[Y|R],[pair(X,Y)|A]) :- pairlists(L,R,A).
pairlists([],[],[]).
arrange([X|L],tree(T1,X,T2)) :-
split(L,X,L1,L2),
arrange(L1,T1),
arrange(L2,T2).
arrange([],void).
split([X|L],X,L1,L2) :- !, split(L,X,L1,L2).
split([X|L],Y,[X|L1],L2) :- before(X,Y), !, split(L,Y,L1,L2).
split([X|L],Y,L1,[X|L2]) :- before(Y,X), !, split(L,Y,L1,L2).
split([],_,[],[]).
before(pair(X1,_),pair(X2,_)) :- X1 < X2.
numbered(tree(T1,pair(_,N1),T2),N0,N) :-
numbered(T1,N0,N1),
N2 is N1+1,
numbered(T2,N2,N).
numbered(void,N,N).
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