Function well_formed 

fn well_formed<T: NodeType>(
    fragment: &AvidmGf2DisperseShareFragment<T>,
) -> Result<EpochNumber, VidFragmentError>

The fragment’s epoch, if the fragment is structurally sound.

An honest disperser sends epoch and target_epoch equal. They are separately chosen by whoever sent the fragment and select committees on different paths downstream – epoch the leader and share verification, target_epoch the erasure parameters the reconstructor holds every peer’s share to – so a fragment that lets them diverge is malformed.