Inner subroutines have access to the local variables of the outer subroutine that called them. Locally scoped variables and subroutine names are lowercase with infix underscores. FORTRAN does not have a main subroutine or function. The Fortran 90 subroutine is provided in Ref. The algorithm is frequently used as a subroutine in other algorithms. Wilkes is also credited with the idea of symbolic labels, macros and subroutine libraries. Locations , , and are 16-bit parameters for the subroutine named . This allows the caller to omit that argument when calling the subroutine. The arguments of the called subroutine are left in the remaining local registers. Quicksort gained widespread adoption, appearing, for example, in Unix as the default library sort subroutine. These commonly include a "call" or use of a subroutine, object, class, or prototype. BLAS was used to implement the linear algebra subroutine library LINPACK. It defines a subroutine called "Main". This can be useful when passing the address of an array element to a subroutine. Every operation is implemented using the Access(Node v) subroutine.