**Defined in theory: Kif-numbers****Source code: kif-numbers.lisp**

**Documentation:**The term {tt (cis $tau$)} denotes the complex number denoted by $cos(tau) + i sin(tau)$. The argument is any non-complex number of radians.

**Arity:**2**Domain:**Number**Range:**Complex-number

(=> (Cis ?Radians ?Complex) (Not (Complex-Number ?Radians)))