The ratio of public debt to GDP is amazing when it is decomposed.
GDP since 2009 was down by more than 20%. During this period the debt has not grown so much.
In other words, the profile of the ratio of Public Debt to GDP reflects mainly the drop of the economic activity. This is the consequence of the austerity policy that was imposed to Greece by the troika. (See here for the Greeks’ effort)
We can then understand that the debt relief discussion that will come after the agreement on yesterday’s proposals by Tsipras is just a counterpart of this persistent austerity.
Source Paul Krugman (see here)