Function define

define(
...rule: (((...x: number[]) => number) | ((...x: number[]) => number)[])[],
): ChalkboardFunction
Defines a mathematical function in the field of real numbers.
Parameters
- ...rule: (((...x: number[]) => number) | ((...x: number[]) => number)[])[]
  The rule(s) of the function
Returns ChalkboardFunction
Example
```
const parabola = Chalkboard.real.define((x) => x * x - 4);
const y = Chalkboard.real.val(parabola, 3); // Returns 5
```
- Defined in Chalkboard.real.ts:139