@Override
	public String toString() {
		return format(_tree);
	}
Return the string representation of this {@code MathExpr} object. The
string returned by this method can be parsed again and will result in the
same expression object.
{@snippet lang="java":
 final String expr = "5.0 + 6.0*x + sin(x)^34.0 + (1.0 + sin(x*5.0)/4.0) + 6.5";
 final MathExpr tree = MathExpr.parse(expr);
 assert tree.toString().equals(expr);
}

@return the expression string
jenetics.prog/src/main/java/io/jenetics/prog/op/MathExpr.java