Consider a system with three input signals:

ref, a square wave with a period of $1$ microsecond$(1),$ and

two natural number a and b

The system generates a square wave, f$,$ with period equal to $($a $+$ b$)$ microseconds, as shown in figure.

Which of the following algorithms describe the system?

$(1)$ Variable "ref$\_$positive$\_$edge" takes the value TRUE when a positive edge of signal "ref" arrives, and FALSE otherwise.