What is *theoretical number of unique operators* ?

Question

Algorithms

Good time of the day.
I am writing a program that is a combination of several quantitative metrics, incl. Halsted metrics.
The metric itself prepologaet counting the number of operators and operands in the program code. But there are also parameters:
- *theoretical number of unique operators*
- * -"- operands *
Can anyone guess what this is?

Answer 1

Well, let's say the program:
It has one binary operator `+` and two operands - 2 and 3. In the program
- One unary operator -
- One binary +
- Two binary **
Respectively operands:
- a, 2; b, 2
- (a**2 + b**2)
I'm not sure, but it seems to me that the latter should also be considered as a separate operand. Not?

Answer 2

And where did these "theoretical" parameters come from? As far as I remember, Halsted himself used only "number of operators" and "number of operands" to calculate the complexity of the program code