History doesn't matter.
Cells are good, files are bad, URLs are ugly. Checksums are forever.
Code is just another kind of input.
Keeping the checksum is enough, if you can look up the value later.
Always resubmit your entire computation.
All state is in cells, unless it is ephemeral.
As above, so below.
Errors can happen, but wrong answers are unforgivable.
Random generators must not be random.
More than two floating numbers don't add up, nor do they multiply
Execution takes as long as it has to.
Unchanging libraries can be imported. Changing libraries must be included.
Structures hold, schemas validate, classes manipulate.
APIs and GUIs are good, unless they hide things away.
Edit all state, then edit the editor.