A.57 library(terms): Term manipulation
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Availability::- use_module(library(terms)).(can be autoloaded)
Sourceterm_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)].