function f(x) = x && x is unary or binary?

Question

I am currently studying Boolean algebra, here is what I learned from school ( If I understand correctly):

• A Boolean function of one variable (input): unary boolean function.

• A Boolean function of two variables (input): binary boolean function.

• A Boolean function of n variables (input): n-ary boolean function.

and

• ! is a unary Boolean function

• &&, ∥ are binary Boolean functions

So my question is if I have a function f(x) = x && x, is this unary or binary?

Answer 1

There is one variable $x$ so it is unary.