A symbol followed by () usually means that the symbol is a function name. However, it could be an object whose type implements invoke(). Whatever parameters are in the parentheses get passed as parameters to invoke().

Here, we have the same algorithm that we used with the div() function, but this time the function is invoke() instead of div(). We can now "call a function" directly on a String and pass an Int parameter.

You can learn more about this in:
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