Internal definitions are recommended instead of `let` expressions, to reduce nesting.

This `if` expression can be refactored to an equivalent expression using `and`.

This use of `case-lambda` is equivalent to using `define` with optional arguments.

The `apply` function accepts single arguments in addition to a trailing list argument.

The `displayln` function can be used to display a value with a newline after it.

Internal definitions are recommended instead of `let` expressions, to reduce nesting.

This `map` operation can be replaced with a `for/list` loop.

This `for-each` operation can be replaced with a `for` loop.