[tromp]

I wanted to have a definition that's independent of evaluation strategy, and thus somewhat more robust. It also makes it easier to comprehend and verify results, such as a(36) corresponding to Church numeral n=2^2^2^3, of size 5*n+6 bits, where I would have a hard time figuring out how long a left-to-right eager evaluation would take. That is indeed closer to the conventional definition of BB(n) as number of consecutive 1s on output on halting.