i just realised you'll mistake 6 as 9 in some fonts but you'll never mistake 69 with 96

and as i write this i realised 66 and 99 is no go

and as i write that i realised one could have a competitive programming problem with this, like "given n strings made entirely with 6s and 9s, calculate the number of the ones that one won't mistake as a different number (e.g. 6699 but not 66999 (which could be mistaken as 66699 when read upside down))"