+ Order(pow(x, 2));
result += check_series(e, 0, d, 2);
+ e = sqrt(1+x*x) * sqrt(1+2*x*x);
+ d = 1 + Order(pow(x, 2));
+ result += check_series(e, 0, d, 2);
+
+ symbol a("a");
+ e = pow(x, 4) * sin(a) + pow(x, 2);
+ d = pow(x, 2) + Order(pow(x, 3));
+ result += check_series(e, 0, d, 3);
+
return result;
}