The functions in section~#seclists#10900> <#10901#>consume<#10901#> lists that contain
atomic data, especially numbers, symbols, and booleans. But functions must
also be able to <#10902#>produce<#10902#> such lists. Furthermore, they must be able
to consume and produce lists that contain structures. We discuss these
cases in this section, and we continue practicing the use of the design
recipe.