Returns all contiguous subsequences of a list (including the empty one).
Subsequences[list]
Subsequences[list, n]
Subsequences[list, {n}]
Subsequences[list, {nmin, nmax}]
Subsequences[list, nspec, s]
Subsequences[list, nspec, {s}]
Subsequences[{a, b, c}]
→ {{}, {a}, {b}, {c}, {a, b}, {b, c}, {a, b, c}}