There is no particular reason. For instance, we can hold the function constant in one variable and get two more variants of the function, \\( \chi_m(n) \\) and \\( \chi_n(m) \\).

Edit

**Hint:** Hold the variable \\(m\\) constant at zero, and consider the function \\( \chi_0(n) \\) . What possible value or values does this function produce on positive values of \\(n\\)? What possible value or values does this function produces on negative values of \\(n\\)?