System.out.println("\n\nBuild ASTNode by hand\n");
formula_base = new ASTNode(Math.PI);
System.out.println("\npi formula = " + formula_base.toFormula());
System.out.println("pi formula = " + formula_base.toMathML());
System.out.println("pi formula = " + formula_base.toLaTeX());
System.out.println("pi formula = " + formula_base.toString());
System.out.println("\n\nBuild ASTNode by formula\n\n");
formula_base = ASTNode.parseFormula("pi");