Analysis of information sources in references of the Wikipedia article "Reform of the date of Easter" in English language version.
This is a translation of Milankovitch, 1923
the Western churches took a step towards the Orthodox side by agreeing to keep the ancient rule, while in earlier discussions they had tended to propose a third way (…) by suggesting to fix the date of Easter on a specific Sunday in April.
He said that Easter should most likely be fixed for the second or third Sunday of April