Omega Nebula and Horseshoe Nebula

It's always fun when a philosophy examples comes up in real life. Last night, I first saw the Omega Nebula in one part of the sky. About an hour or so later, I saw the Horseshoe Nebula in another part of the sky. It was only today that I realized that horseshoes and omegas have the same shape, and checked, and found that in fact the two are the same (the sky had rotated during that hour, so the (relative) locations were different). Of course, it is a necessary truth that the Omega Nebula = the Horseshoe Nebula (necessarily x=x). But it was a truth I only discovered on comparing the Messier and NGC catalogs on my PDA. :-)