A.6.P.RI:5.1 - Preserve a displacement across orientations

A faces north and asks B to displace a crate one metre in the direction A calls left. B faces south. The assignment is to preserve the external displacement, and both headings are known.

The source direction is west. For B, facing south, west is right. The receiving instruction is therefore to move the crate one metre to B’s right. If B turns east before acting, west becomes backward. Copying “left” would now send the crate north.

Change the assignment to “move the crate one metre toward your own left”. With B facing east, the correct displacement is now north. The known headings did not settle the instruction; the preservation condition did.

If B’s heading is unavailable, “one metre west” can still be a complete instruction for a performer who can act in that frame. Otherwise the body-relative instruction remains unresolved. The method asks for the information needed by the chosen means, not for every possible position description.

A mobile robot receiving the same external displacement needs a usable relation between the shared frame and its action representation. Obtaining that relation and the capability to perform the movement is a separate technical task. The example does not prescribe its learning or control architecture.