(* 3 4 5)  // ok, because of associativity
(/ 3 4 5)  // not ok, because of the lack of associativity
(/ 5)      // maybe  1/5 ??? 

(+ 4 5 6)  // ok,   4 + (5 + 6) == (4 + 5) + 6
(+ 5)      // ok, unary "positivity" operator
(- 4 5 6)  // not ok,  (4 - 5) - 6  or  4 - (5 - 6)
(- 6)      // ok, unary negation operator


x + - 5  // addition and negation operators
x + -5   // addition operator, two's-complement negative number

(+ x (- 5))  // addition and negation operators
(+ x -5)     // addition operator, two's-complement negative number


(+ 4)
(+ 4 5)
(+ 4 5 6)
(+ 4 5 6 7 8)

        +        // the interperter iterate through all the branches and accumulates the sum
    / / | \ \
   / /  |  \ \
  4 5   6  7  8



(@ 4 5)  // error

    @
   / \
  4   5


x  // error


(/ 3 4 5)  // error


for (int i = 0; i < 1_000_000_000; i++)
{
   (/ i x)  // an interpreter checks this 1,000,000,000 times
}