Function Reference: F
    @fact	Factorial function.
 
    @factlog	Natural logarithm of the factorial function.
 
    @fdist	Upper tail of F-distribution.
 
    @fill	Vector initialized from a list of values.
 
    @first	The first non-missing value in the vector or series.
 
    @firstsby	First non-missing value in a series for each specified group.
 
    @floor	Largest number less than or equal to with optional precision.
 
    @fracdiff	Fractional difference of series data.
 
    @fv	Future value of annuity payments and (optional) initial lump sum receipt.