# Casting Out 9s/Historical Note

It appears in Bhaskara II Acharya's Lilavati, dating from about $1150$.
It arrived in Western Europe from the Arabs, via the Liber Abaci of $1202$ by Leonardo Fibonacci.
When initially invented, the technique involved dividing the numbers involved by $9$ and adding the remainders, but the summing of the digital roots has the same effect.