C#, LINQ IQueryable.Where의 조건을 쉽게 만들기

http://social.msdn.microsoft.com/Forums/en-US/linqprojectgeneral/thread/925b245d-5529-4a64-8cd4-4bc83ee6fe7a/

 public static class PredicateBuilder
{
    public static Expression<Func<T, bool>> Make<T>() { return null; }
    public static Expression<Func<T, bool>> Make<T>(this Expression<Func<T, bool>> predicate)
    {
        return predicate;
    }
    public static Expression<Func<T, bool>> MakePredicate<T>(this IQueryable<T> source)
    {
        return null;
    }
    public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr, Expression<Func<T, bool>> or)
    {
        if (expr == null) return or;
        var invokedExpr = Expression.Invoke(or, expr.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>(Expression.Or(expr.Body, invokedExpr), expr.Parameters);
    }
    public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr, Expression<Func<T, bool>> and)
    {
        if (expr == null) return and;
        var invokedExpr = Expression.Invoke(and, expr.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>(Expression.And(expr.Body, invokedExpr), expr.Parameters);
    }
}