[Fact] public void Test5_custom()
 => Assert.Equal(
     MathS.Interval(4.5, true, "6", false),
     (4.5, true, "6", false).ToInterval()
     );
 [Fact] public void Test6()
 => Assert.Equal(
     MathS.Interval("6", 3),
     ("6", 3).ToInterval()
     );
 [Fact] public void Test4()
 => Assert.Equal(
     MathS.Interval(4.5, 4.5),
     (4.5, 4.5).ToInterval()
     );
 [Fact] public void Test5()
 => Assert.Equal(
     MathS.Interval(4.5, "6"),
     (4.5, "6").ToInterval()
     );
 [Fact] public void Test2()
 => Assert.Equal(
     MathS.Interval(3, "6"),
     (3, "6").ToInterval()
     );
 [Fact] public void Test1_custom()
 => Assert.Equal(
     MathS.Interval(3, true, 4.5, false),
     (3, true, 4.5, false).ToInterval()
     );
 [Fact] public void Test0()
 => Assert.Equal(
     MathS.Interval(3, 3),
     (3, 3).ToInterval()
     );
 [Fact] public void Test7()
 => Assert.Equal(
     MathS.Interval("6", 4.5),
     ("6", 4.5).ToInterval()
     );
 [Fact] public void Test6_custom()
 => Assert.Equal(
     MathS.Interval("6", true, 3, false),
     ("6", true, 3, false).ToInterval()
     );