Amud 63b

And the witnesses testify that he ate it - והעדים מעידים אותו שאכלו

Summary:
There is no כפל by the claim of אבד even if it is destroyed; there is כפל by טוען טענת גנב even if the item is בעין.

One should say; the verse is discussing one who claims, it was stolen - הוי אומר בטוען טענת גנב דבר הכתוב

Summary:
We derive the content of a verse from a neighboring verse.

From, ‘thief’; ‘the thief’ - מגנב הגנב

Summary:
הגנב (as opposed to גנב) means a special or unique גנב.

And the other one maintains that הגנב is for the ruling of רחב"א, etc. - ואידך הגנב לכדרבי חייא בר אבא

Summary:
One may use the same word either to include or to exclude depending on the context.