4.2 The arguments

• Then the brackets enclose the arguments of the function (x, y = NULL etc).
• The argument x has no default value, however the argument y has the default setting of NULL which means that if the analyst does not supply any value for y when the function is called, then y = NULL.
• Likewise uiw has no default whereas liw does. If liw is not supplied then it will take the value of uiw.