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Calling Built-in Functions

   To call a built-in function, write the name of the function followed
by arguments in parentheses.  For example, `atan2(y + z, 1)' is a call
to the function `atan2', with two arguments.

   Whitespace is ignored between the built-in function name and the
open-parenthesis, but we recommend that you avoid using whitespace
there.  User-defined functions do not permit whitespace in this way, and
you will find it easier to avoid mistakes by following a simple
convention which always works: no whitespace after a function name.

   Each built-in function accepts a certain number of arguments.  In
most cases, any extra arguments given to built-in functions are
ignored.  The defaults for omitted arguments vary from function to
function and are described under the individual functions.

   When a function is called, expressions that create the function's
actual parameters are evaluated completely before the function call is
performed.  For example, in the code fragment:

     i = 4
     j = sqrt(i++)

the variable `i' is set to 5 before `sqrt' is called with a value of 4
for its actual parameter.