<#4#>initial environment<#4#> <#5#>top level environment<#5#>
This chapter describes Scheme's built-in procedures. The initial (or ``top level'') Scheme environment starts out with a number of variables bound to locations containing useful values, most of which are primitive procedures that manipulate data. For example, the variable <#6#>abs<#6#> is bound to (a location initially containing) a procedure of one argument that computes the absolute value of a number, and the variable <#7#>+<#7#> is bound to a procedure that computes sums.