I am reading an article about rigidity of surfaces in Minkowski space time and i am having big trouble for finding references about the topic.
I have been working with the material and definitions from the volume 5 chapter 12 of the Spivak Comprehensive Introduction to differential Geometry. There i can find at least the basic definitions, but it is more for the case of embedded surfaces (dimension 2 manifold) in $\mathbb{R}^3$ and there are many important differences in co-dimension 2 that is the case i am working in.
I would appreciate if anyone knows a good reference about this topic.