6 Using Operators Operators are similar to commands in that they are also used to manipulate objects. Unlike commands, however, operators have their own syntax and you cannot define new operators of your own—you can only use the operators that are already built into AppleScript itself. AppleScript has 25 operators in total. These include math operators that allow you to perform simple math calculations on numerical objects, comparison operators that let you compare two objects to see if they are the same or different, and a very handy “concatenation” operator that you can use to join two strings or two lists together.
However, did you know that many of these applications also have a second interface, one that’s invisible to ordinary human users but can be freely accessed by other Mac OS X applications running on the same or even other machines? This invisible interface allows one Mac application to take control of another—for example, to open a file, manipulate its content, and save it again. In some cases, applications may interact in this way purely for their own benefit; for example, the operating system occasionally tells all the currently running applications to quit themselves so that it can safely shut itself down.
A semilinear Schrödinger equation in the presence of a magnetic field by Arioli G., Szulkin A.