Should I do a correction / corrigendum?
How do you make corrections to a published paper?
Opacity problem over white object in Illustrator I have a problem. I'm working with an object at 50% opacity. When it's over the artboard itself the color looks great, but when I put a white object behind it I get this weird color that doesn't look accurate.  This happens with every object and only in CMYK. I'm pretty sure this never happened to me before so maybe I changed something in the settings or I don't know.  Does anyone have any idea? Defining the Product of Ideals Where does the &quot;naive definition&quot; of the product of two ideals $I$ and $J$, $IJ = \{ ij \mid i \in I, j \in J \}$ fall apart? (The product of two ideals $I$ and $J$ is defined to be $IJ := \sum_i a_ib_i$, where each $a_i$ is in $I$ and each $b_i$ is in $J$.)  Note: This is a question from a problem set I'm working on. I am not expecting a full solution for the answers, but I'd like some help knowing where to look. It seems to work fine in $\mathbb{Z}$ and $\mathbb{C}[x]$. VBA Hide Rows that contain N/A htaccess subdomain Case field mapping with custom object fields? On November 11, my American girlfriend flew over to the UK to visit me. She was detained and questioned, and refused entry under the belief she would not leave within those six months. This was due to her having no return flight booked, as we were going to wait until we were together in the UK to book a return flight for either herself, or both of us back to the USA once we decided what exact dates I would be able to travel. Lesson learned. A hard lesson, but we learned!  Anyway, they said although she'll flag up in the future, it won't be a straight ban from entering and she could even try to come back the next day if she so pleased, although it would be unwise if her circumstances had not changed.  Fast forward to December 18. She got herself a job in the States to prove she intends to leave at the end of her stay, and has since applied for a UK Standard Visitor Visa. She posted her documents off to New York earlier today.  Will they send her a letter back refusing to issue her a visa since, as an American citizen, she does not even need one? She wanted to get one to be safe as I told her not to fly to the UK even with return flights booked if she doesn't have a visa, as she risks being denied once again after a long flight. It's hard to get this information on the Internet, and some stories I read said that they were sent a letter back from the UK Embassy denying their visa simply because they don't need one in the first place - even after that person was denied entry.  We're in a bit of a pickle granted, so any help would be greatly appreciated.   Cheers. How do I determine the size of my array in C?   That is, the number of elements the array can hold? $\hbar \rightarrow 0$ in quantum mechanics We often see a limit $\hbar \rightarrow 0$ in quantum mechanics and sometimes it's related with symmetry breaking. Can someone briefly write the story behind this limit? Most efficient way to check for DBNull and then assign to a variable? This question comes up occasionally, but I haven't seen a satisfactory answer.  A typical pattern is (row is a DataRow):   if (row["value"] != DBNull.Value)  {       someObject.Member = row["value"];  }   My first question is which is more efficient (I've flipped the condition):    row["value"] == DBNull.Value; // Or   row["value"] is DBNull; // Or   row["value"].GetType() == typeof(DBNull) // Or... any suggestions?    indicates that .GetType() should be faster, but maybe the compiler knows a few tricks I don't?  Second question, is it worth caching the value of row["value"] or does the compiler optimize the indexer away anyway?  For example:    object valueHolder;   if (DBNull.Value == (valueHolder = row["value"])) {}   Notes:   row["value"] exists. I don't know the column index of the column (hence the column name lookup). I'm asking specifically about checking for DBNull and then assignment (not about premature optimization, etc.).   I benchmarked a few scenarios (time in seconds, 10,000,000 trials):  row["value"] == DBNull.Value: 00:00:01.5478995 row["value"] is DBNull: 00:00:01.6306578 row["value"].GetType() == typeof(DBNull): 00:00:02.0138757   Object.ReferenceEquals has the same performance as "=="  The most interesting result? If you mismatch the name of the column by case (for example, "Value" instead of "value", it takes roughly ten times longer (for a string):  row["Value"] == DBNull.Value: 00:00:12.2792374   The moral of the story seems to be that if you can't look up a column by its index, then ensure that the column name you feed to the indexer matches the DataColumn's name exactly.  Caching the value also appears to be nearly twice as fast:  No Caching: 00:00:03.0996622 With Caching: 00:00:01.5659920   So the most efficient method seems to be:   object temp;  string variable;  if (DBNull.Value != (temp = row["value"]))  {       variable = temp.ToString();  } What should the order of DNS servers be for an AD Domain Controller and Why? This is a  about Active Directory DNS Settings. Related:     Assuming an environment with multiple domain controllers (assume that they all run DNS as well):  in what order should the DNS servers be listed in the network adapters for each domain controller? Should 127.0.0.1 be used as the primary DNS server for each domain controller? Does it make any difference, if so what versions are affected and how? I downvoted  and now really can't say why, so I wanted to remove my downvote. However, I get the message:  You last voted on this question yesterday Your vote is now locked in unless this question is edited  Why is this? I don't think I voted on it multiple times, and even when I did, I can change my mind, can't I? Okami is now reborn in High Definition for PS3. The graphics are obviously better, sharper and yet preserves the gist of the original game, however I can swear some of the texts have changed as well.  My PS2 console is no longer available to me so I can't test it myself, but does anyone know whether there are any changes to the game (aside from graphics) or not? Replacements for switch statement in Python? Cyclic Group Generators of Order $n$ We don't get much snow in the UK, so I don't have much experience photographing it, and when I tried photographing falling snow last year I found it very hard to capture the snowflakes in the air — they either didn't show up or were just streaks. Is there a shutter speed that is best for this? I don't want to use flash to do so.  Any other snow photography tips welcome from those in snowier places! How to prove this binomial identity $\sum_{r=0}^n {r {n \choose r}} = n2^{n-1}$? I am trying to prove this binomial identity $\sum_{r=0}^n {r {n \choose r}} = n2^{n-1}$ but am not able to think something except induction,which is of-course not necessary (I think) here, so I am inquisitive to prove this in a more general way.  The left side of an identity occurs while solving another problem (concerning binomial theorem) so I am more interested in deriving the right side from the left side, else I have to remember it now onward.  EDIT: I am more interested in an algebraic proof rather than combinatorial argument or something involving calculus (however I liked  and  solution), hence I am removing the combinatorics tag. How to handle WndProc messages in WPF? In Windows Forms, I'd just override WndProc, and start handling messages as they came in.  Can someone show me an example of how to achieve the same thing in WPF? Ruby Style: How to check whether a nested hash element exists Health effect of electromagnetic and acoustic waves on brain function What's the term when you ask a question which implies a lie?