... Adler, M Bazin, M Schiffer, Introduction to General Relativity , Mc.Graw-Hill 1965 R M Wald, General Relativity , Univ of Chicago Press 1984 P.A.M Dirac, General Theory of Relativity , Wiley Interscience ... constructions to describe forces between elementary particles or other branches of fundamental physics This is why in an introduction to general relativity it is of importance to separate as ... occur To enable us to this we introduce another type of vectors: the so-called contra-variant vectors and tensors Since a contravariant vector transforms differently from a covariant vector we...