At the Open Door.

In front of the open door to the next floor, Saeon looked back. The display stand in the science area was visible. Their corrected explanation remained beside the observation boards.

Today was the end-of-term move-up challenge. Math and science occupied two areas on the same floor. Saeon remembered the words they had placed in the science area before the door opened.

Back then, Saeon had been opening the triangular folding board. Sodam put the piece box farther onto the shelf. Dure opened the honey-colored notebook beside the blank explanation space.

“Let's finish today's display ourselves.”

Saeon tapped the folding board's edge. They wanted to leave an explanation. Beside it, Saeon kept room for the others to add their words.

Teacher Gwak stood beside the low observation bench. The wide hallway stayed open behind the friends. There was no heating equipment on the bench.

“Keep the record as it is. Finish the explanation.”

A clear plastic observation container sat inside a round base. Its top was open, with liquid water remaining inside. There was no need to lift or move it.

Two observation boards stood beside it. One held before-and-after pictures of the same container. The other listed conditions and recorded changes.

The water in the before picture was higher than in the after picture. No lumps filled the empty space above either water level. The actual water matched the after picture's height.

The conditions said normal classroom temperature. They had started with liquid water, without ice. It hadn't been boiled, spilled, or wiped away.

The record also said it hadn't been moved to another container. The change line said some liquid water at the surface had changed into water as a gas. They weren't guessing the cause from the water level alone.

First, Saeon lined up the before-and-after pictures. The two container bottoms were level. The lower water and the empty space above it showed together.

Saeon remembered erasing only when it boils last time. This time, they could write a good explanation without those words. Saeon started with one line on the folding board.

“This matches the record.”

Saeon held the words in front of the display stand. But the empty space above the water caught their eye. Saeon wanted people looking at it to see the change.

Below the first line, Saeon added more words.

Beside the words, Saeon drew a round lump. They lined it up above the water in the picture. With a shape in the explanation, the change seemed clearer.

“They can see what it changed into here.”

Dull amber strands wrapped around the door to the next floor. The knot of light reached the observation boards' edges. Cream-colored eye-like gaps appeared inside its round outline.

A Gate Tangle. A device made from a mistaken idea. No strands touched the water or its container. The pictures and recorded words stayed visible.

The outer folds looked like a neat board frame. Inside, bent strands lay over one another. No light stretched into the hall behind them.

Sodam lowered a hand from the glasses.

“Hang on. Where did you see that lump?”

Saeon stopped pushing the folding board. The recorded before picture had no lump. Neither did the after picture. That round shape was only in Saeon's drawing.

If they couldn't see it, did that mean nothing had changed?

Saeon took the folding board away from the stand. Last time, Saeon had changed the water height to fit a guess. This time, a guess had filled the empty space.

“I drew it. It isn't in the record.”

Dure opened a palm in front of the notebook.

“Here. There's still the explanation.”

The fingertip pointed to the picture without a lump. Then it moved to the record about the change to gas. Saeon looked at both places together.

“Just saying we can't see it isn't the end.”

Saeon stopped before erasing the lump. The line about water changing to gas had nearly been erased with it. Dure's hand stayed beside those words.

Sodam began with the conditions on the observation board.

“No boiling. Nobody spilled or wiped it away.”

Next came the change line.

“Some liquid water at the surface changed into gas.”

Saeon found those same points on the folding board. The first line matched the record. The words added after it were making that first line shaky.

“What if you have to see a white lump?”

Sodam's hand stopped in the empty space above the picture. Saeon looked at the shape that hadn't been erased yet. Then they would be saying a change happened only if they could see the gas.

“I'd think it had to boil so I could see it again.”

Saeon read the words aloud. The first line said boiling wasn't needed. The second demanded a visible shape.

Saeon had brought back an old mistake in new words. The folding board tipped toward them. Now the places to erase and the places to keep looked different.

Sodam pointed between the conditions and the change line.

“It changes without boiling. Water vapor itself is invisible.”

A thin cream-colored pin reached from the fingertip. The observation board's smooth strand stopped. The overlapping inner folds stayed in place, too.

Saeon erased the lump and the second line. The first line stayed. The recorded picture's empty space stayed empty, too.

“I wanted to show it, so I added a shape that wasn't there.”

Saeon wrote new words beneath the first line. Before simply copying Sodam, Saeon looked at the container. What they could see was the liquid water left inside.

“We can see the water that's left. We can't see the gas it changed into.”

Saeon wrote water vapor beside water as a gas. Under that went invisible. No words pointing to a white lump remained.

“So visible mist isn't the water vapor itself.”

Saeon didn't fill the empty space with a shape. The words explaining the change went beside the picture. Invisible didn't mean gone.

Dure traced along the bottoms of the before-and-after pictures, stopping at the after picture's lower water level. Then the fingertip moved to the line about the change to gas.

“We kept what was seen. We kept the changed state, too.”

The fingertip reached the end of the corrected explanation.

“No boiling needed. The gas is invisible.”

Saeon waited until Dure finished. The hand ready to stand up the folding board stayed before the base. Dure swept a fingertip once along the page's edge.

“If those two fit the record, we're done.”

Saeon stood the corrected folding board on the display stand. Sodam opened a gap to keep the words below visible. Dure recorded the same container's before-and-after pictures in the notebook.

Looking at the teacher, Saeon pointed to the new words.

“I thought we could see the gas, so I drew a shape. But that picture wasn't in the record.”

Saeon showed the empty space where the lump had been erased.

“Water vapor is water as a gas. Water vapor itself is invisible.”

Sodam opened a hand before the condition line.

“Some water at the surface changed into gas even though it wasn't boiled.”

Sodam pointed between the new explanation and the record.

“It doesn't need to boil. And we don't need to see the gas.”

Dure opened the notebook all the way to the end.

“We didn't change the pictures. The explanation has the changed state, too.”

Dure rested a fingertip beneath the stand.

“We checked both. We can finish here.”

The teacher kept both hands down while the three spoke. Saeon let go of the folding board, too. Only after the friend's last words had ended.

The final knot around the observation boards loosened. The science strands around the door unraveled and came down, too. The loose cream-colored strands lay straight across the boards.

The water remained in its container. No light rose above the water. Saeon looked at the empty gap between the boards and the container.

Evaporation is liquid water changing into water vapor at its surface. It happens without boiling, too. Saeon added the change's name at the end of the corrected words.

The little result light at the front of the base came on. When the recess beside it opened, Saeon bent down. Both hands stayed lowered outside it.

A real little stone stair piece with three steps lay inside. The tiny hollow above its top step was full of blue light. There was still no stone in that spot.

The stair piece lifted a little from the recess floor. Blue light flowed beneath it.

The light followed the floor toward the door to the next level. The piece left the base's recess and set off to the right. Saeon's eyes followed it as it started.

“This piece moved, too.”

The little recess's cover closed after the piece left. Saeon straightened. From the bench, the inside of the threshold was hard to see clearly.

Sodam and Dure didn't follow the piece, either. The corrected explanation and open records lay before them. Saeon lined up the display stand's bottom edge.

Dure briefly opened the records of earlier activities. Objects beside a magnet. Poles facing each other. Ice and water. Saeon followed the drawings already on those pages.

No new problems appeared. The three arranged the records and display words to leave behind. The observation container stayed inside its base.

That was the science activity Saeon was remembering. After their explanation in the math area, Saeon had also watched the knots unravel around the table and door. Now the unraveled light from both places remained before them.

The great spread of light when the door opened had happened once. The hands that started in science and carried on in math had been under that same light. Saeon remembered the names changing within it.

Putting something down first didn't mean finishing alone. Beside Saeon's record, there had been room for a friend to point. Saeon remembered the hand sliding the folding board aside.

Sodam held the piece box, already closed. The conditions checked today remained in both areas. Saeon watched as Sodam stayed beside them instead of going back to check more.

The notebook Dure hugged held both boards and explanations. That hand had chosen where the final words belonged. Saeon looked at the fingers resting on the book's edge.

The display had changed in order inside that light. There wasn't another moment of Growth in the other area. After the Growth display vanished, the same notice had appeared.

“Nice and clear.”

The teacher's short words stayed in the doorway.

Saeon turned toward the space beyond the open door. Behind lay the hall they could return through and the finished display. Ahead, wide stairs continued beside the railing.

“Let's go up.”

Sodam came alongside, and Dure arrived with the notebook held close. All three walked together inside the railing. On the first step, Saeon looked up.

The light returning around the pieces came back to mind. A connection to the top was still only a guess. Saeon looked toward the heights they couldn't see.

What was at the top?