It's hard to remember the details of how many operands each of these procedures takes and what kinds of numbers they can be applied to.

Yes, it's kind of a nuisance, but in practice common sense will keep you from running into most of the theoretically possible problems. Here's a summary table that you can copy and consult if you're worried about making a mistake:

```procedure     arity          operand types
---------------------------------------------------------------------------
+             0 or more      integers, rationals, reals, or complex numbers
-             1 or 2         integers, rationals, reals, or complex numbers
*             0 or more      integers, rationals, reals, or complex numbers
quotient      2              integers (second operand non-zero)
remainder     2              integers (second operand non-zero)
modulo        2              integers (second operand non-zero)
abs           1              integer, rational, or real
max           1 or more      integers, rationals, or reals
min           1 or more      integers, rationals, or reals
gcd           0 or more      integers
lcm           0 or more      integers
---------------------------------------------------------------------------
```
A procedure's arity is simply the number of operands to give it.

This document is available on the World Wide Web as

`http://www.math.grin.edu/~stone/scheme-web/arity.html`

created June 25, 1995
last revised December 26, 1995