Create a logarithm out of a custom base and a lower limit.

Input parameters:

1. B → Logarithm base. Must be a positive number which is not extremely close to zero.
2. L → Lower limit of logarithm domain. Logarithms typically have a lower limit at zero, but this can adjusted by moving the entire function left or right.
3. Z → Optional x-intercept of the function. When omitted, the limit+1 is used.

Output parameters:

1. Fn → Logarithm function.