// use transformers to simplify expressions
var transformers = new List<ExpressionTransformer>
{
    new ConditionTransformer(),
};

var simplifier = new ExpressionSimplifier(transformers);

// (a, b) => Not(Not((((Not(Not((IIF(((a == b) OrElse True), 4, 7) == 7))) == False) AndAlso (((6 - a) == 8) OrElse Not(((5 - a) == 8)))) AndAlso (Not(((5 - a) == 8)) OrElse Not(((6 - a) == 8))))))
Expression<Func<int, int, bool>> expr =
    (a, b) => !!(
        !!(((a == b || true) ? 4 : 7) == 7) == false
        && (6 - a == 8 || !(5 - a == 8))
        && (!(5 - a == 8) || !(6 - a == 8)));

Console.WriteLine($"Original: {expr}");
Console.WriteLine($"Simplified: {simplifier.Simplify(expr)}");
// Output: (a, b) => ((6 - a) == 8)