Theorem If a, b, and c are vectors and c is a scalar, then
1. a !! b = -b !! a
2. (ca) !! b = c(a !! b) = a !! (cb)
3. a !! (b + c) = a !! b + a !! c
4. (a + b) !! c = a !! c + b !! c
5. a !! (b !! c) = (a !! b) !! c
6. a !! (b !! c) = (a !! c)b - (a !! b)c