✅ How to group by tautology with LINQ?

IEnumerable<Row> rows =
[
    new Row(null, "_or_", null, null),
    new Row(null, "_or_", true, true),
    new Row(null, "_or_", false, null),
    new Row(true, "_or_", true, true),
    new Row(true, "_or_", false, true),
    new Row(false, "_or_", false, false),

    new Row(null, "or", null, null),
    new Row(null, "or", true, true),
    new Row(null, "or", false, null),
    new Row(true, "or", true, true),
    new Row(true, "or", false, true),
    new Row(false, "or", false, false),

    new Row(null, "xor", null, null),
    new Row(null, "xor", true, null),
    new Row(null, "xor", false, null),
    new Row(true, "xor", true, false),
    new Row(true, "xor", false, true),
    new Row(false, "xor", false, false),
    new Row(null, "xor_", null, null),
    new Row(null, "xor_", true, null),
    new Row(null, "xor_", false, null),
    new Row(true, "xor_", true, false),
    new Row(true, "xor_", false, true),
    new Row(false, "xor_", false, false)
];