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 with its environment. For example, it can construct and operate foraging systems to procure fuel or materials, waste disposal systems, or transporters to carry replica shops to other locations.

Obviously, self-replication of such an extended system requires replication of the program-memory. This memory can be partitioned into two parts: (1) The self-replication process memory, and (2) the external process (manufacturing) memory. The distinction between these two memories is that the first is required to reproduce the basic unit (shop machines plus factons) while the second memory contains the program to produce process equipment not essential to the self-replicating nucleus.

At this point it is clear that the effect of a self-replicating system on its environment may take many forms dependent on the external process program. Using such a program, the scope of the system can be extended by construction of machines and structures capable of producing complex subsystems including mineral processing plants, solar energy power supplies, etc.

All of these extended self-replicating systems would embody the same basic nucleus of machines, factons and self-replication programming. They would differ only by addition of the external process program segment peculiar to each type.

Reliability and redundancy. Reliability is a primary concern, especially in the case of self-replicating processes. Two ideas are most important here.

First, the self-replicating program accuracy can be verified by comparison with other replicas of the same program. If a discrepancy is found between two self-replicating programs, a third or fourth replica can be consulted and the error pinpointed and corrected. The test of correctness is the ability to self-replicate.

Second, machines tend to wear, and ultimately to fail, from excessive use. On the other hand, if the system can replicate itself it can make spare parts and install them itself. A special program segment, the "maintenance program," should be devised to check machine wear and perform repairs as needed. This segment would be part of the self-replication program, although another somewhat similar maintenance program should probably be used to care for machines and structures of the external process. This external maintenance program would be specialized for each extended system and is properly part of the second memory.

Speciation. Any self-replicating system is actually another species of SRS, the species being dependent upon the contents of the second memory.

A group of interacting extended self-replicating systems may form a still larger self-reproducing system with yet more complex capabilities. It is not immediately apparent what factors limit the possibilities of such systems. Separable subsystems manufactured by a self-replicating shop may be machines of considerable complexity, themselves incapable of self-replication. Their supply is therefore dependent on the self-replication shop and its program.

It is interesting to note that a facton equipped with an aberrant program may function like a virus, visiting a self-replicating shop and using its machines for reproduction of its own type without constructing any other machine. It could then replicate its program for installation in the new "virus facton" and reproduce this way, using materials and energy from a host self-replication shop. This possibility opens up a large field of problems related to the security of self-replication systems from facton defect or infection.