Some KKE voters were saying they would switch votes to Syriza in a second election.

BBC: Greece: Trying to understand Syriza

One current obstacle to this is the KKE's historic enmity to Syriza and indeed the entire rest of the Greek left.

BBC: Greece: Trying to understand Syriza

But in the early 1990s the main Moscow-oriented KKE quit the alliance, purging about 45% of its members, who then stayed inside Synaspismos with the Eurocommunists.

BBC: Greece: Trying to understand Syriza

And that is Mr Papandreou's gamble - that nobody outside the KKE will present a coherent alternative to a yes vote, and that the KKE does not want power.

BBC: Greek referendum is coin-flip on euro exit

The success of Syriza then seems down to its ability to attract voters and activists from all these groups, eating into almost every part of the left including the old Moscow-style KKE.

BBC: Greece: Trying to understand Syriza

Under Tsipras' leadership, and invigorated by now including the entire left, except the traditionalist KKE, Syriza grew the far left's vote from 3.3% to 5.6% in the 2007 election - giving it 14 MPs.

BBC: Greece: Trying to understand Syriza

Even without a majority, a Syriza-DL minority could attempt a legislative programme that relied on the abstention of some of Pasok's remaining MPs, tacit "non-opposition" form the KKE, and, paradoxically, the non-opposition of the right-wing anti-austerity partiy Independent Greeks (conservative nationalist).

BBC: Greece: Trying to understand Syriza

The KKE gained 26 seats.

BBC: Greece: Trying to understand Syriza