Note that we slightly extend the syntax of conditional statements described in section 1.3.2 by allowing another conditional statement in place of the block following else.
 We have used 0.001 as a representative small number to indicate a tolerance for the acceptable error in a calculation. The appropriate tolerance for a real calculation depends upon the problem to be solved and the limitations of the computer and the algorithm. This is often a very subtle consideration, requiring help from a numerical analyst or some other kind of magician.
 This can be accomplished using error, which takes as argument a string that is printed as error message along with the number of the program line that gave rise to the call of error.
 Try this during a boring lecture: Set your calculator to radians mode and then repeatedly press the $\cos$ button until you obtain the fixed point.
 $\mapsto$ (pronounced maps to) is the mathematician's way of writing lambda expressions. $y \mapsto x/y$ means y => x / y, that is, the function whose value at $y$ is $x/y$.
1.3.3 Functions as General Methods