Every morning at 5.30am, Mr. Tan Liang opens his

flat in Block 78, Tiong Bahru, to find chalk

dust on his pillow — but he doesn’t teach. Not

anymore. Not since the blackout.

The war ended in ’45, but the Japanese air raid

on Tiong Bahru in ’53 never got cleared. The

government buried the dead in mass graves,

sealed the block, and moved everyone out. Except

the ghosts. They stayed. And they kept doing

their sums.

Mr. Tan remembers nothing before last Tuesday.

Not his wife. Not his son. Not why he’s holding

a red pen with “Nanyang University” engraved on

the cap. But the blackboard in his living room?

It’s covered in calculus problems — solved

correctly, in perfect Chinese script — with

margins written in Malay and Tamil. Only the

dead students from ’53 knew how to do that.

His tuition agency fired him last week. Said

he’d “stopped charging.” He didn’t remember

teaching. But the HDB neighbours? They bring him

nasi lemak at 7pm. “You used to tutor their

children,” says Mrs. Lim, wiping her eyes. “Even

the ones who died.”

The rule: no one can teach in Tiong Bahru Block

78 after 9pm. Not even ghosts. The Housing Board

put it up in ’54. No one knows why. But every

night at 9.01, the lights flicker. The chalk

erases itself. And the walls whisper in three

languages.

Last night, he woke up to the sound of a girl

reciting quadratic formula in Singlish. “A plus

B squared minus four AC, boss, like how you pay

rent.” He laughed. He hadn’t laughed since

before the blackout.

He went to the block’s basement. Found a rusted

metal box. Inside: his old teaching licence. His

son’s birth certificate. And a photo — him,

kneeling, holding a dying boy with a broken leg,

while three other children scribbled on his

shirt with chalk. The date: 17 March 1953.

He remembers now.

He was the tuition teacher who stayed behind

after the bombing. Taught the dying kids their

Olevels so they wouldn’t forget. Died himself

when the ceiling caved.

But the HDB didn’t bury him.

They sealed the block.

And the ghosts? They kept his lesson going.

Now, at 6am, he opens the door. The chalkboard

is blank.

On the floor, a single piece of paper: “Tuition

fees: S$5. Pay in kaya toast.”

He smiles.

Buys the toast.

Starts writing.

The first line: “Let x = the cost of forgetting

your mother.”

The wall behind him giggles.