input: Please answer the following: Information: - An arch is a curved structure that spans a space and may or may not support weight above it. Arch may be synonymous with vault, but a vault may be distinguished as a continuous arch forming a roof. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture, and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures. - The Aniene, formerly known as the Teverone, is a river in Lazio, Italy. It originates in the Apennines at Trevi nel Lazio and flows westward past Subiaco, Vicovaro, and Tivoli to join the Tiber just north of Rome. It thus formed the principal valley east of ancient Rome and was an important water source as the city's population expanded. The falls at Tivoli were noted for their beauty. Historic bridges across the river include the Ponte Nomentano, Ponte Salario, and Ponte di San Francesco, all of which were originally fortified with towers. - A boot is a type of footwear and a specific type of shoe. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is clearly distinguishable from the rest of the sole, even if the two are made of one piece. Traditionally made of leather or rubber, modern boots are made from a variety of materials. Boots are worn both for their functionality protecting the foot and leg from water, extreme cold, mud or hazards (e.g., work boots may protect wearers from chemicals or use a steel toe) or providing additional ankle support for strenuous activities with added traction requirements (e.g., hiking) and for reasons of style and fashion. - The Ponte di San Francesco ( Italian for Bridge of Saint Francis ) is a medieval segmental arch bridge over the Aniene in Subiaco , Lazio , Italy . Constructed in 1358 , its single span measures 37 metres ( 121 ft ) . Other notable historic bridges crossing the Aniene include the ancient Ponte Nomentano and Ponte Salario , both of which were also fortified with a tower . - Italy, officially the Italian Republic, is a unitary parliamentary republic in Europe. Located in the heart of the Mediterranean Sea, Italy shares open land borders with France, Switzerland, Austria, Slovenia, San Marino and Vatican City. Italy covers an area of and has a largely temperate seasonal climate and Mediterranean climate; due to its shape, it is often referred to in Italy as "lo Stivale" (the Boot). With 61 million inhabitants, it is the fourth most populous EU member state. - An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct (a long bridge) may be made from a series of arches, although other more economical structures are typically used today. - A viaduct is a bridge composed of several small spans for crossing a valley, gorge, marshland or forming a flyover. The term "viaduct" is derived from the Latin "via" for road and "ducere", to lead. The ancient Romans did not use the term; it is a modern derivation from an analogy with aqueduct. Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length. Viaducts may span land, water or both. - The Ponte Salario, also called Ponte Salaro during the Middle Ages, is a road bridge in Rome, Italy, whose origins date back to the Roman period. In antiquity, it lay outside the city limits, 3km north of the Porta Collina, at the point where the Via Salaria (modern SS4) crossed the Aniene, a tributary of the Tiber. The visible side arches are assumed to originate from the first stone structure built during the 1st century BC. - A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague. - TheMediterranean Sea (pronounced ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant. The sea is sometimes considered a part of the Atlantic Ocean, although it is usually identified as a separate body of water. What entity does 'ponte di san francesco' has the relation 'material used' with?
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output: stone

input question: Information: - Nitrogen dioxide is the chemical compound with the formula . It is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. At higher temperatures it is a reddish-brown gas that has a characteristic sharp, biting odor and is a prominent air pollutant. Nitrogen dioxide is a paramagnetic, bent molecule with C point group symmetry. - Nitryl fluoride , NO2F , is a colourless gas and strong oxidizing agent , which is used as a fluorinating agent and has been proposed as an oxidiser in rocket propellants ( though never flown ) . It is a molecular species , not ionic , consistent with its low boiling point . The structure features planar nitrogen with a short N - F bond length of 135 pm . - Nitryl is the nitrogen dioxide (NO) moiety when it occurs in a larger compound. Examples include nitryl fluoride (NOF) and nitryl chloride (NOCl). What entity does 'nitryl fluoride' has the relation 'instance of' with????
output answer:
chemical compound