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Subprogram linkage semantics requires many action by the implementation. Simple subprograms have relatively basic actions. Stack-dynamic languages are more comple. Subprograms with stack-dynamic local variables and nested subprograms have two components. Activation record instances contain formal parameters and local variables among other things. Static chains are the primary method of implementing accesses to non-local variables in static-scoped languages with nested subprograms. Access to non-local variables in dynamic-scoped languages can be implemented by use of the dynamic chain or thru some central variable table method.