Wry neck, or torticollis, is a painfully twisted and tilted neck. The top of the head generally tilts to one side while the chin tilts to the other side. This condition can be congenital (present at birth) or acquired. It can also be the result of damage to the neck muscles or blood supply. Wry neck sometimes goes away without treatment.
In the quaternions, 0 is the additive identity. In the ring of functions from R to R, the function mapping every number to 0 is the additive identity. In the additive group of vectors in Rn, the origin or zero vector is the additive identity.
Before we jump into the definition of the additive identity property, however, let's review our number system. The diagram below shows the different types of numbers: There are three major categories of numbers: real, imaginary and complex. Real numbers are all the numbers that you can plot on a real-number line.