Nobody knew where he came from, if that was even the right way of wording it. One day they noticed him, living in an abandoned park on the outskirts of the city. The wonderful park had hillocks, widely spaced trees of silver and golden leaves, abstract and natural sculptures, shallow streams of crystal, and an assortment of gates, blackboards and machinery. The mathematician wandered around, opening and closing gates, writing with chalk on the blackboards and building, mending and rebuilding his machinery. The mathematician loved to speak of the chalk, its powdery white atoms, the way chalk adhered to the board one minute or would blow off into the wind the next, the way the chalk held together to make each integer and formula, or how it fused into a thin film when brushed. On certain days, they came to see him write on a great blackboard. Whenever he wrote on it, fireworks and magic lanterns revolved around him, words and numbers burned in the air and diffused into their faces with an affectionate warmth, and everyone went home afterwards, filled, peaceful and whole. For years, the mathematician taught the children, especially the poor ones, how to add, subtract, divide, multiply, how to factor, use decimals and find roots. Through logic, arithmetic, algebra, geometry, calculus, trigonometry, statistics and even physics, they wandered on a magic journey with him, through the known and unknown that only grew in both distance, wholeness, and intimacy. Engineers, carpenters, cobblers and blacksmiths came to him for advice. Even scholars, philosophers and doctors from the city and other cities learned some of his secrets, although most were too vast to take in. The mathematician helped them keep their books, maintain records, draw plans for building walls or bridges, and charted stars and maps for them. The city grew wealthy. One day, the mathematician vanished. Some say he was murdered; some say he escaped; some say he was exiled. Many accused him of all manner of crimes, while stripping the park of his blackboards and machinery. Those machines that were too mysterious or too great to haul were robbed of parts or vandalized. Most of what they took home they did not know how to use. They were able to reproduce some fireworks and build other kinds of machinery, but after a while the blackboards and machines were returned to the abandoned park, where they began to rust. A legend grew up that the mathematician was only a dream sent by some diabolical magic or plague. The citizens concocted various theories to rationalize the leftover machinery. Some even tried to burn blackboards or melt down gears to destroy the relics. Time passed. The children would go to the abandoned park to play. They built their own machines from scraps and tried to learn from the machines that were more or less intact. They whispered and wrote on blackboards, and some even claimed to have seen magic lanterns, fireworks and the ghost of the mathematician return, walking from blackboard to blackboard, opening and closing gates, blowing enchanted chalk dust from his hands into the north wind.