As for the reverse scheme "the Ukrainian way," it is as follows. Russian gas transits through Ukrainian territory to Europe. When it passes through Ukrainian territory, it is withdrawn by Naftogaz. With the mutual consent of the Ukrainian side and the European consumer, this gas is not considered withdrawn, but "reversed". In other words, the European buyer "sells" this gas to the Ukrainian side.
It is important to note that the pipeline through which gas can be delivered from Europe to Ukraine does not physically exist. That is why the reverse is called "virtual".
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