Russia and Ukraine exchanged 205 prisoners of war on Friday, hours after rescue workers ended their search of a destroyed block of flats in Kyiv in which 24 people were killed, including three girls. Most of the Ukrainian prisoners had been held since 2022, said President Zelensky. The swap was part of a short-lived ceasefire ending this week with the launch of massive Russian strikes across Ukraine, including a missile attack that reduced 18 flats to rubble. Among the victims was 12-year-old Lyubava Yakovleva, whose father was killed during the war. Meanwhile, Russian officials said four people, including a child, were killed when Ukrainian drones hit the city of Ryazan, south-east of Moscow.

Kim Jong Un praises troops who'self-blasted' to avoid capture by Ukraine Kim Jong Un has praised North Korean soldiers who killed themselves by detonating their grenades while fighting for Russia against Ukraine, confirming a long-suspected battlefield policy. In a speech this week, the North Korean leader said those who unhesitatingly opted for self-blasting, suicide attack, in order to defend the great honour were heroes. South Korea estimates at least 15,000 North Koreans have been sent to help Russia recapture parts of western Kursk, and more than 6,000 have been killed so far. Neither Pyongyang nor Moscow have confirmed the numbers. Intelligence agencies and defectors have said the soldiers were under Pyongyang's orders to kill themselves rather than be taken prisoner by Ukraine.

Nobel Peace Prize winner Narges Mohammadi has been handed further prison sentences of seven-and-a-half years by an Iranian court, her lawyer has said. The human rights activist was sentenced to six years for gathering and collusion, and one-and-a-half years for propaganda activities by a court in the north-eastern city of Mashhad, Mostafa Nili announced on social media on Sunday. Mohammadi was arrested in December for making provocative remarks at a memorial ceremony, Iranian authorities said at the time. Her family said she was taken to hospital after being beaten during the arrest . The 53-year-old was made a Nobel laureate in 2023 for her activism against female oppression in Iran.

What is in the 28-point US plan for Ukraine? 'Ukraine is running out of men, money and time' Can the US get all sides to end the war? Why is Europe opposing Trump's peace plan? Two people were killed in a Ukrainian drone strike on the Russian city of Saratov, regional Governor Roman Busargin said in a statement on Telegram. An unspecified number of people were also injured in the attack.

An oligopoly is a market in which the price of goods is controlled by a few firms. Cournot introduced the simplest game-theoretic model of oligopoly, where profit-maximizing behavior of each firm results in market failure. Furthermore, when the Cournot oligopoly game is infinitely repeated, firms can tacitly collude to monopolize the market. Such tacit collusion is realized by the same mechanism as direct reciprocity in the repeated prisoner's dilemma game, where mutual cooperation can be realized whereas defection is favorable for both prisoners in a one-shot game. Recently, in the repeated prisoner's dilemma game, a class of strategies called zero-determinant strategies attracts much attention in the context of direct reciprocity. Zero-determinant strategies are autocratic strategies which unilaterally control payoffs of players by enforcing linear relationships between payoffs. There were many attempts to find zero-determinant strategies in other games and to extend them so as to apply them to broader situations. In this paper, first, we show that zero-determinant strategies exist even in the repeated Cournot oligopoly game, and that they are quite different from those in the repeated prisoner's dilemma game. Especially, we prove that a fair zero-determinant strategy exists, which is guaranteed to obtain the average payoff of the opponents. Second, we numerically show that the fair zero-determinant strategy can be used to promote collusion when it is used against an adaptively learning player, whereas it cannot promote collusion when it is used against two adaptively learning players. Our findings elucidate some negative impact of zero-determinant strategies in the oligopoly market.