[Fact] public void TestIntegral2Args2() => Assert.Equal(2 * MathS.Integral("x + 2", "x"), FromString("2 integral(x + 2, x)"));
[Fact] public void Integral5() =>
Test(@"\int \left[{x}^{23}-x_{16}\right] d\left[xf\right]", MathS.Integral("x^23-x_16", "xf"));
[Fact] public void Integral3() =>
Test(@"\int \left[x+1\right] d\left[xf\right]", MathS.Integral("x + 1", "xf"));
[Fact] public void Integral4() =>
Test(@"\int \left[\frac{1}{x}\right] d\left[xf\right]", MathS.Integral("1/x", "xf"));
[Fact] public void Integral2() =>
Test(@"\int \int \left[x+1\right] dx dx", MathS.Integral("x + 1", x, 2));