So now this hard shine has polka-dots, but that's interesting in its own right too. Shine shine - aha! She gets one to come free. Bops it around the room. It is nearly invisible unless it's on a surface, but it can go straight between any two points.

Helen can make shines to Lu's specifications fairly trivially while she reads. As she does she requests a pencil and paper to work on practice programs.

"They're not normally mobile. I can make them co-occupying a space with something, but that is...unpleasant on a sensory level that probably wouldn't make sense to you. And yes, it does harm the things."

"Do you mind if I try it with something?"

"...Do you mean you want me to make a light co-occupying a thing. Um. I appreciate that science is important here but it's really really unpleasant so please think about what level of discomfort you would be willing to deal with in order to perform this experiment and then tell whether I should still do it."

"I mean I want to get an apple from Bar and try to send a hard shine through it so I know what happens. How unpleasant would it be? I wouldn't want to, say, be crippled until the next time I die for this result, since I can experiment after I've gotten them home. But it matters for what kinds I want - if they're a disaster to touch at speed, I probably shouldn't use them as vehicles unless I'm manually piloting and never let anyone I don't trust puppet one for themselves, if they disintegrate if I run one into something then I don't have to be so careful about who I let handle them except insofar as I'd need to beware my supply, etcetera."

"Oh. If you just want to hit something really hard with one you've got then go for it."

The apple is bumped. It moves in response to the thing nudging at it.

Lu stabilizes the apple and rams the shine at it at visible but rapid speed.

The apple goes splat. A piece of apple lands on Helen's cheek and she wipes it off absentmindedly.

Lu picks up the top half of the apple off her lap. "So they will cut things if they go fast enough, but they're not really sharp..." She holds down the bottom apple half, guides the shine at it to see what speed it needs to bite into the peel when the apple won't nudge easily.

It doesn't need speed as such. If the apple won't nudge then continuing to press into it will result in the apple yielding.

She turns the shine and pushes with the flat side.

This will squash it a little and push it out of her hand if she applies enough pressure.

"Okay. So these would be hazardous to use as ground-level vehicles unless I can program them sufficiently well and they can see things they aren't touching..." She writes down her results and starts experimenting with running them into each other at various angles and speeds.

If they run into each other they will mostly bounce off. They don't suffer damage from the collisions.

She can, if she's very alert to timing, make them just stop when they hit instead of bouncing back, but she cannot make them damage, intersect, break, or pass through each other.

That's correct, she can't. It's not that difficult to make them just stop, but it does require some degree of attention so long as she is manually piloting them.

Helen will pay attention to this part, since ultimately 3D syntax is going to be more useful to her than the regular kind.

Lu shows her the notes she's got on how she needs to revise the standard syntax. (It's all in natural language, to a point, just standardized for easy error-checking; it is not necessary to write a new shine operating system.) Shines normally have directions designated with an array of symbols, conventionally shortening "north south east west" even though they will retain the mapping of directions to sides after turning - at least that's what the book says; it turns out Lu prefers abbreviations for "bow stern starboard port" (as translated by Milliways. She has added "mast" and "keel" for, loosely, up and down. There is no way to draw the new directions into a flat instruction sheet, so Lu has written a short program introduction describing "mast" as the direction away from the side of the shine reading the instructions and "keel" as towards the instructions. Likewise, she has to describe pitch and roll. (Yaw is handled just fine with conventional shine instructions; it's just called turning.) "It's possible that after I've been working with these long enough they'll embed into the natural language without further explanation and I'll be able to use them plain. Which will be important if I want to give them long complicated instructions."

"This is a lot like computer science. I wonder if studying that will help. There's no way I'm going to learn all of this in the time we spend here, and Bar says the book won't be comprehensible once I leave the premises."

"I don't know. What's computer science?"