Hysteresis has historically been a bigger threat in the euro area than in America or Britain.

ECONOMIST: The crunch may entrench unemployment

So the next line of defence against hysteresis is to keep the jobless in the labour force, actively looking for work.

ECONOMIST: The crunch may entrench unemployment

Admittedly, cyclical increases in unemployment may become permanent if labour-market rigidities, such as strict hiring-and-firing laws, make it hard for the jobless to find work even when the economy recovers, a condition known as hysteresis.

ECONOMIST: Should we learn to love recessions?