The classic game theory dilemma where two prisoners are individually offered a deal if they’ll betray the other prisoner. But if they both betray each other then it’s bad news for both of them. What they choose depends on what they think the other will choose.

The prisoner’s dilemma

Idempotence is essentially an operation that, no matter how many times you do it, you’ll still get the same result, at least without doing other operations in between. A classic example would be view_your_bank_balance being idempotent, and withdraw_1000 not being idempotent. It’s a property that’s often handy as you can retry the operation without worrying about unintended effects.

Idempotence is a concept from mathematics and computer science but can be applied more generally. For example, simple on and off buttons are idempotent, a property that can be very useful in emergencies.

Idempotence

‘Tis the season for these powerful things. Turns out sneezes can travel up to 8 m, coughs up to 6m and they can linger in the air for up to 10 minutes.

All the more important to make sure you’re doing your Dracula sneeze into your sleeve.

Sneezes and coughs