Fortunately, there is a way to get around the duplication problem entirely. Let's take a cue from how a perfume makes a strong impression first, but then appears to fade away, or how, when you put your hand in water that is very hot or very cold, the sensation is intense at first — but will soon disappear almost entirely. As we say, we get used to these sensations. Why? Because our senses react mainly to how things change in time. This is true even for the sensors in our eyes — though normally we're unaware of it because our eyes are always moving imperceptibly. Most of the sensory agents that inform our brains about the world are sensitive only to various sorts of time changes — and that, surely, is also true of most of the agents inside the brain.
Any agent that is sensitive to changes in time can also be used to detect differences. For whenever we expose such an agent, first to a situation A and then to a situation B, any output from
that agent will signify some difference between A and B.
This suggests a way to solve the duplication problem. Since most agents can be made to serve as difference-agents, we can compare two descriptions simply by presenting them to the same agency at different times. This is easily done if that agency is equipped with a pair of high-speed, temporary K-line memories. Then we need only load the two descriptions into those memories and compare them by activating first one and then the other.
Store the first description in pronome p. Store the second description in pronome q. Activate p and q in rapid succession. Then any changes in the agents' outputs represent differences between A and B!
We can use this trick to implement the scheme we described for escaping from a topless-arch. Suppose that p describes the present situation and q describes a box that permits no escape. Each Move agent is designed to detect the appearance of a wall. If we simply blink
from the present situation to the box frame, one of these agents will announce the appearance of any box wall that was not already apparent in the present situation. Thus, automatically, this scheme will find all the directions that are not closed off. If the outputs of the Move agents were connected to cause you to move in the corresponding direction, this agency would lead you to escape!
The method of time blinking can also be used to simplify our difference-engine scheme for composing verbal expressions, since now the speaker can maintain both p and q inside the selfsame agency. If not for this, each speaker would need what would amount to a duplicate society of mind in order to simulate the listener's state. Although the method of time blinking is powerful and efficient, it has some limitations; for example, it cannot directly recognize relations among more than two things at a time. I suspect that people share this limitation, too — and this may be why we have relatively few language-forms, like between and middle, for expressing three-way comparisons and relationships.