Input: Group (mathematics)
Finite symmetry groups such as the Mathieu groups are used in coding theory, which is in turn applied in error correction of transmitted data, and in CD players. Another application is differential Galois theory, which characterizes functions having antiderivatives of a prescribed form, giving group-theoretic criteria for when solutions of certain differential equations are well-behaved.u[›] Geometric properties that remain stable under group actions are investigated in (geometric) invariant theory.

What concept investigates geometric elements that stay stable under group action?
Output: invariant theory

Input: London
Some international railway services to Continental Europe were operated during the 20th century as boat trains, such as the Admiraal de Ruijter to Amsterdam and the Night Ferry to Paris and Brussels. The opening of the Channel Tunnel in 1994 connected London directly to the continental rail network, allowing Eurostar services to begin. Since 2007, high-speed trains link St. Pancras International with Lille, Paris, Brussels and European tourist destinations via the High Speed 1 rail link and the Channel Tunnel. The first high-speed domestic trains started in June 2009 linking Kent to London. There are plans for a second high speed line linking London to the Midlands, North West England, and Yorkshire.

In what year did the Channel Tunnel open?
Output: 1994

Input: Protestantism
World literature was enriched by the works of Edmund Spenser, John Milton, John Bunyan, John Donne, John Dryden, Daniel Defoe, William Wordsworth, Jonathan Swift, Johann Wolfgang Goethe, Friedrich Schiller, Samuel Taylor Coleridge, Edgar Allan Poe, Matthew Arnold, Conrad Ferdinand Meyer, Theodor Fontane, Washington Irving, Robert Browning, Emily Dickinson, Emily Brontë, Charles Dickens, Nathaniel Hawthorne, Thomas Stearns Eliot, John Galsworthy, Thomas Mann, William Faulkner, John Updike, and many others.

Samuel Taylor is listed as enriching what?
Output: World literature

Input: Oklahoma City
In 2008, Forbes magazine named Oklahoma City the most "recession proof city in America". The magazine reported that the city had falling unemployment, one of the strongest housing markets in the country and solid growth in energy, agriculture and manufacturing. However, during the early 1980s, Oklahoma City had one of the worst job and housing markets due to the bankruptcy of Penn Square Bank in 1982 and then the post-1985 crash in oil prices.[citation needed]

What year did forbes list Oklahoma city as "recession proof".
Output:
2008