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Predicate term_factorized/3
 term_factorized(+Term, -Skeleton, -Substiution)
Is true when Skeleton is Term where all subterms that appear multiple times are replaced by a variable and Substitution is a list of Var=Value that provides the subterm at the location Var. I.e., After unifying all substitutions in Substiutions, Term == Skeleton. Term may be cyclic. For example: 
?- X = a(X), term_factorized(b(X,X), Y, S).
Y = b(_G255, _G255),
S = [_G255=a(_G255)].
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Jan Wielemaker said (2014-05-07T07:04:19):0 upvotes 0 0 downvotes
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Note that the results of this predicate are independent from the actual sharing and cycles that appear in the term. For example:

?- term_factorized(a(x(1),x(1)), T, S).
T = a(_G1475, _G1475),
S = [_G1475=x(1)].

Factorized cycles are guaranteed to have the minimal cycle length. For example:

?- A = [1,2,1,2|A], term_factorized(A, T, S).
A = [1, 2, 1, 2|A],
S = [T=[1, 2|T]].

The complexity of this predicate is O(N*log(N)), where N is the size of the term.