Answer:
A presupposition is something you suppose to be the case before you even start something. Therefore the first act of anything cannot by definition be a presupposition to the action of the play.
If you are asking whether or how the action in the first act is necessary for the understanding of the rest of the play, this is, I am afraid to tell you, the case in any well-written play. The first act of every play introduces the main characters and lays out what their problems are, which are worked out in the succeeding acts and a final conclusion reached at the end. As Aristotle said, "Every play must have a beginning, a middle, and an end." He was a master of the obvious, Aristotle was.