Pica

Pica had grown up in a weaving town, watching her aunt read pattern-cards — cards punched with the lengths of each colored stripe. Her aunt never guessed where a stripe went. She'd measure the longest stripe against the width of the cloth and say, "This one's so wide it can only sit here, near enough," and mark the part that couldn't move.

The first time Pica did it herself she was small and impatient and wanted to fill the whole row at once. Her aunt caught her hand. "You'll fill a cell you'll have to pull out," she said. "Fill only what has to be filled. Mark what has to be blank. The picture comes when you stop reaching past what you know."

It was the hardest lesson and the one that stuck. Certainty first. The rest follows the certain part like thread follows a needle.

Ada saw her fill a corner of a Nonogram nobody had cracked and knew right away. "You're not painting," Ada said. "You're proving."

"Every filled cell I place, I can tell you why it can't be blank," Pica said. "Every blank I place, I can tell you why it can't be filled. The clue-numbers do the arguing. I just listen."

Her method is overlap and edges. A long run in a narrow line barely moves, so its overlap is huge — big blocks of certain cells. A run pinned against the edge (a clue that starts a line, with the run touching the wall) is exact. And once a run is placed for sure, the cell right after it must be blank — you can't have two runs touching. Those forced blanks then squeeze the next run, which reveals its own overlap, and the picture walks itself open, cell by justified cell.

A girl was filling a Picross by vibes — a cell here because it "felt" like part of the shape.

"What's the clue on that column?" Pica asked.

"Three, then two."

"How many cells?"

"Ten."

"Three, a gap, two — that's at least six cells of pattern in ten. Slide it left as far as it goes, slide it right as far as it goes. Where does the three overlap itself?"

The girl worked it out on her fingers. "The… middle of the three is filled both ways. One cell for sure."

"One cell you'll never have to erase," Pica said. "Build out from the cells you can defend. Never from a feeling." The girl marked her one certain cell, then the forced blank beside the finished run, and suddenly the column had edges to push against, and the two came clear a breath later.