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Predicate scanl/4
 scanl(:Goal, +List, +V0, -Values)
 scanl(:Goal, +List1, +List2, +V0, -Values)
 scanl(:Goal, +List1, +List2, +List3, +V0, -Values)
 scanl(:Goal, +List1, +List2, +List3, +List4, +V0, -Values)
Scan an ensemble of m (0 <= m <= 4) lists of length n head-to-tail ("scan-left"), using columns of m list elements as arguments for Goal. The scanl family of predicates is defined as follows, with V0 an initial value and V the final value of the scanning operation: 
scanl(G, [X_11, ..., X_1n],
         [X_21, ..., X_2n],
         ...,
         [X_m1, ..., X_mn], V0, [V0, V1, ..., Vn] ) :-
   call(G, X_11, ..., X_m1, V0, V1),
   call(G, X_12, ..., X_m2, V1, V2),
   ...
   call(G, X_1n, ..., X_mn, V<n-1>, Vn).

scanl behaves like a foldl that collects the sequence of values taken on by the Vx accumulator into a list.

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