Just define it using \newtheorem like you have done for environment theorem:
The amsthm isn't the best on its own; however, thmtools provides a really neat 'front-end' for amsthm and other theorem packages.
In particular, thmtools includes a prefoothook and postfoothook which ...
If one systematically needs different theorems definitions in the same documents, egreg approach is convenient. But many of us might have a mymath.tex with common shortcuts and settings, which is a ...
You can do something like this
Here are two approaches. First, you can combine \ref and \nameref to format as desired. Second, you can use \mylabel to save preformatted text. The advantage of the latter is that it is implemented ...