The ubiquitous occurrence of the exponential function in pure and applied mathematics has led mathematician W. Rudin to opine that the exponential function is "the most important function in mathematics". In applied settings, exponential functions model a relationship in which a constant change in the independent variable gives the same proportional change (that is, percentage increase or decrease) in the dependent variable. [Courtesy of Wikipedia] Applied to Catholicism, the independent variable, we might say, is God's call, the percentage increase or decrease of which, however, might or might not be proportional to the change in the dependent variable. Here is a list of surprising dependent variables.

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https://en.wikipedia.org/wiki/Category:Converts_to_Roman_Catholicism