Problem: John von Neumann:

The axiomatization of mathematics, on the model of Euclid's Elements, had reached new levels of rigour and breadth at the end of the 19th century, particularly in arithmetic, thanks to the axiom schema of Richard Dedekind and Charles Sanders Peirce, and geometry, thanks to David Hilbert. At the beginning of the 20th century, efforts to base mathematics on naive set theory suffered a setback due to Russell's paradox (on the set of all sets that do not belong to themselves). The problem of an adequate axiomatization of set theory was resolved implicitly about twenty years later by Ernst Zermelo and Abraham Fraenkel. ZermeloFraenkel set theory provided a series of principles that allowed for the construction of the sets used in the everyday practice of mathematics. But they did not explicitly exclude the possibility of the existence of a set that belongs to itself. In his doctoral thesis of 1925, von Neumann demonstrated two techniques to exclude such setsthe axiom of foundation and the notion of class.

Who resolved the problem of adequate axiomatization of set theory?
---
A: Ernst Zermelo and Abraham Fraenkel

Problem: After Cassander's death in 298 BCE, however, Demetrius, who still maintained a sizable loyal army and fleet, invaded Macedon, seized the Macedonian throne (294) and conquered Thessaly and most of central Greece (293-291). He was defeated in 288 BC when Lysimachus of Thrace and Pyrrhus of Epirus invaded Macedon on two fronts, and quickly carved up the kingdom for themselves. Demetrius fled to central Greece with his mercenaries and began to build support there and in the northern Peloponnese. He once again laid siege to Athens after they turned on him, but then struck a treaty with the Athenians and Ptolemy, which allowed him to cross over to Asia minor and wage war on Lysimachus' holdings in Ionia, leaving his son Antigonus Gonatas in Greece. After initial successes, he was forced to surrender to Seleucus in 285 and later died in captivity. Lysimachus, who had seized Macedon and Thessaly for himself, was forced into war when Seleucus invaded his territories in Asia minor and was defeated and killed in 281 BCE at the Battle of Corupedium, near Sardis. Seleucus then attempted to conquer Lysimachus' European territories in Thrace and Macedon, but he was assassinated by Ptolemy Ceraunus ("the thunderbolt"), who had taken refuge at the Seleucid court and then had himself acclaimed as king of Macedon. Ptolemy was killed when Macedon was invaded by Gauls in 279, his head stuck on a spear and the country fell into anarchy. Antigonus II Gonatas invaded Thrace in the summer of 277 and defeated a large force of 18,000 Gauls. He was quickly hailed as king of Macedon and went on to rule for 35 years.
When did Cassander die?
---
Answer: 298 BCE

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
A variety of industries benefit from hunting and support hunting on economic grounds. In Tanzania, it is estimated that a safari hunter spends fifty to one hundred times that of the average ecotourist. While the average photo tourist may seek luxury accommodation, the average safari hunter generally stays in tented camps. Safari hunters are also more likely to use remote areas, uninviting to the typical ecotourist. Advocates argue that these hunters allow for anti-poaching activities and revenue for local communities.[citation needed]
What kind of camps do ecotourists usually stay in?
A: unanswerable

Context and question: Hydrogen is highly soluble in many rare earth and transition metals and is soluble in both nanocrystalline and amorphous metals. Hydrogen solubility in metals is influenced by local distortions or impurities in the crystal lattice. These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas's high solubility is a metallurgical problem, contributing to the embrittlement of many metals, complicating the design of pipelines and storage tanks.
What influences hydrogens solubility in metals?
Answer: local distortions or impurities in the crystal lattice

Question: Present-day Slavic people are classified into West Slavic (chiefly Poles, Czechs and Slovaks), East Slavic (chiefly Russians, Belarusians, and Ukrainians), and South Slavic (chiefly Serbs, Bulgarians, Croats, Bosniaks, Macedonians, Slovenes, and Montenegrins), though sometimes the West Slavs and East Slavs are combined into a single group known as North Slavs. For a more comprehensive list, see the ethnocultural subdivisions. Modern Slavic nations and ethnic groups are considerably diverse both genetically and culturally, and relations between them even within the individual ethnic groups themselves are varied, ranging from a sense of connection to mutual feelings of hostility.
Is there an answer to this question: West and East Slavs are sometimes combined into a single group called what?

Answer: North Slavs

Due to the work nature of airline pilots, who often cross several timezones and regions of sunlight and darkness in one day, and spend many hours awake both day and night, they are often unable to maintain sleep patterns that correspond to the natural human circadian rhythm; this situation can easily lead to fatigue. The NTSB cites this as contributing to many accidents[unreliable medical source?] and has conducted several research studies in order to find methods of combating fatigue in pilots.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): Who follows a very natural human circadian rhythem?
Ah, so..
unanswerable