> It really is mind bending how fast this function grows. While the BB function is obviously a well-defined function over the integers, I find it helpful to th

> It really is mind bending how fast this function grows. While the BB function is obviously a well-defined function over the integers, I find it helpful to think of it as a function over qualitatively heterogeneous items—such as stones, bread toasters, mechanical watches, and computers. The key idea is to view the underlying computing devices not as “a little more powerful” than the previous ones, but as fundamentally different kinds of entities.