"Because you came here in the dark to find out why someone else's numbers were working." A beat. "That's not a broken mind. You're a different kind of thinker."
"What kind?"
"High-performance. They've been giving you the wrong fuel."
A pause. "Like a race car?"
"Exactly like a race car."
"Oh." She absorbs this with the gravity it deserves. "Can you fix it? The fuel?"
I'm going to regret this.
"Slide me a clean sheet of paper." I tap the steel bottom of the trade slot.
Lily passes it through the slot.
I draw five squares on the paper. Clean lines, careful spacing, given the dim light and the cold, that's made my fingers stiff. Then three more beside them. I push it back through the slot before I can reconsider.
Her hand takes it the moment it clears the gap. Small fingers, nail-bitten, a smear of something purple on the side of her pinky that might be marker or might be jam.
"Eight." A small, triumphant exclamation comes through the vent.
"What did you do to get that?"
"I counted them." A pause. "All of them. From the beginning." The confession carries the faint defensiveness of someone who suspects there's a better way.
"That's building." I tap my finger on the concrete on my side. "Adding is building. Five blocks and three blocks. You built eight." I wait. "Slide it back."
The paper comes through. I fold three squares under my thumb and push it back.
"Five." The answer is immediate, pre-empting my question.
"What happened to the three?"
A silence with weight in it. The kind that means she's not searching for the answer I want but actually turning the question over.
"I took them away."
"Subtraction is taking away. Addition is building. They're the same operation."
"How?"
"Same road. Different direction."
A pause.
"Oh." The syllable is quiet, like a small door opening.
I draw the number line across the next sheet. Tick marks spaced evenly, zero through twelve, each number sitting on a small circle. I push it through.
"What's that?" The query comes instantly.
"A river." I trace the line with my fingernail, the scratch loud in the narrow gap. "And each number is a stone. A flat rock sticking up out of the water."
A beat. "Okay."
"And there's a dinosaur who lives on this river. He can't swim. He has to hop from rock to rock."
