When I ask the question, what I really mean is ``is there a mechanical structure that guarantees the correct output?'' For example, we can train neural networks to perform functions such as "and", "xor", etc., and convince ourselves the network has "really learned" what it means to calculate the function.

Is that true for interpreting programming languages? If so, a bug isn't just ``I haven't seen a similar enough example''. It reflects a deeper mistake that will likely occur again.