Greece reduced empty vat gap by 61% the last 6 years and is now comparable to the EU average.

What is “empty” in this context? Autocorrected “evaded” in “empty”?
I do guess that vat is not a kind of vessel but a value added tax.

That said: what did greece do to reduce it?
I am familiar with Italian efforts which essentially consisted in tweaking accounting rules so that it was progressively harder to hide off the books transactions, most notably by mandating electronic invoicing that made tax authorities checks instantaneous.