Mark tasks as obsolete
I'd like the possibility to mark tasks as obsolete, "Not Applicable" or some similar term. (as opposed to just tick them off and mark them as "done")
Why? Because then my history will be more accurate. Tasks may appear terrible important when I enter them and later become totally redundant because of other developments.
Example: Right now it is vitally important to contact X to get Y done. I get delegated the task of speaking with X, and add this to my todoist-tasks. However, X is unavailable, and after 3 days the deadline of Y may be passed, or Y may be solved through other actions, or recent develpment has made Z come along, which makes both X and Y totally redundant.
When reviewing my progress it would be nice if the task "contact X" was marked as "NOT DONE", "OBSOLETE" or something similar in history. I like to see that I did have that particular action for a particular time, but I did NOT complete that task.