## halting problem

*A*and its negation

*not A*to both be true. How can this be, and be coherent? What does it all mean?

**Stefan Kopieczek**explores his story.

**Mike Yates**looks at the life and work of wartime code-breaker Alan Turing. Find out what types of numbers we

*can't*count and why there are limits on what can be achieved with Turing machines.