students substitute their digit choices for 'a' and 'b'
with 'a' bigger than 'b'
share their work with their neighbour
what happens for various input pairs, (a, b)?
having established what happens, students will hopefully ask: "why does this work?"
they could try to make up their own 'machines' with the same result
consider what happens when a = b
and when 'a' is less than 'b'
- not just digits
- with 'b' negative