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# Tracking records that could not be processed

`NotCompleted` is a special result type provided by the `scinexus` package. Apps return a `NotCompleted` result when a condition is not met (`FALSE` type) or an unexpected error occurs (`ERROR` type). These objects evaluate to `False`, carry information about the failure, and propagate through composed pipelines so that subsequent steps are skipped.

## A cogent3 example

Below, an app that selects specific sequences returns a `NotCompleted` because the requested sequence `"Mouse"` does not exist in the primate data set.

The `NotCompleted` instance has attributes identifying what data failed,

where the failure occurred

and the reason for the failure