`quadratic-character``a``p`procedure- a
- integer
- b
- integer

Returns the value of the quadratic character modulo the prime

`p`. That is, for a non-zero`a`the number 1 is returned when`a`is a quadratic residue, and -1 is returned when`a`is a non-residue. If`a`is zero, then 0 is returned.If

`a`is negative or`p`is not positive, quadratic-character raises an error. If`p`is not prime, (quadratic-character a p) is indeterminate.This function is also known as the

*Legendre symbol*.> (quadratic-character 0 5) 0 > (quadratic-character 1 5) 1 > (quadratic-character 2 5) -1 > (quadratic-character 3 5) -1

Wikipedia: Legendre Symbol