The problem comes when the icon that it defaults to for printing is a right load, but the only way that envelopes can be loaded is in the center of the tray. I have an HP Colorlaserjet 3600 and an HP Officejet Pro 8600 and both load this way.
A technical definition of a function is: a relation from a set of inputs to a set of possible outputs where each input is related to exactly one output.
Most calculus text books begin with a review of functions. A function is generally described as a mapping from one set of numbers, called the domain of the function, to another set, called the range. In simple form, if you put one number in to the function, you get another number out.