Most of the few existing assisted-suicide laws rely on the principle of active and informed consent to a procedure that may, or will, lead to death.

ECONOMIST: The right to choose to die

David McNair, senior economic justice adviser at the charity Christian Aid, says tax havens are used in a variety of ways, but the general principle - for a business active in a number of countries - is to maximise the amount of profit made by subsidiaries based where taxes are low, at the expense of those based where taxes are high.

BBC: Tax havens: Is the tide turning?

Engineered geothermal systems (EGS) are based on a related principle, but they work even in parts of the world that are not volcanically active, by drilling thousands of metres underground to mimic the design of natural steam or hot-water reservoirs.

ECONOMIST: Inside story: Hot rocks and high hopes | The