The notation tuples(S, N) denotes the
set of n-tuples of length N of elements
taken from the set S, where
N is non-negative. For a given set
S, the set of n-tuples may be defined
inductively as follows:
Specific n-tuples are denoted P = (x₀, x₁, ..., xₙ),
which is essentially shorthand for P = (x₀, (x₁, (... (xₙ, ())))),
with the 0th element of
P being x₀ and
the nth element being
xₙ.