Which recurrence defines the Fibonacci sequence?
an=an−1⋅an−2a_n = a_{n-1} \cdot a_{n-2}an=an−1⋅an−2
an=an−1+an−2a_n = a_{n-1} + a_{n-2}an=an−1+an−2
an=2an−1+an−2a_n = 2a_{n-1} + a_{n-2}an=2an−1+an−2
an=an−1−an−2a_n = a_{n-1} - a_{n-2}an=an−1−an−2