new ASTNode(10)));
ev.createPriority(ASTNode.parseFormula("25"));
ev.createDelay(ASTNode.parseFormula("2"));
ev.createEventAssignment("s1", ASTNode.parseFormula("s2"));
System.out.println("==================================");
new SBMLWriter().write(doc, System.out);
System.out.println("\n==================================");
doc.setLevelAndVersion(2, 4);
System.out.println("==================================");
new SBMLWriter().write(doc, System.out);
}