The external declaration has one of the following forms:
external I1, ..., In
real external I1, ..., In
integer external I1, ..., In
Boolean external I1, ..., In
where each Ik is an identifier and n is any positive integer. A type declarator preceding the declarator external signifies a function procedure having that type. Note that no information about parameters appears in an external declaration. See [Appendix A] for syntactical definition.
In the ALGO mode, LIB cards must be included in the job deck for nonstandard library routines, in addition to the external declarations. Details are found in [Section VIII].
VI. Standard Procedures
Certain procedures are used without being declared. These include the standard functions listed in the Algol 60 report and the input-output and intermediate tape procedures. The complete list is as follows:
ABS