In the article:
S. Fortune, J. Hopcroft, J. Wyllie, The directed subgraphs homeomorphism problem, Theoret. Comput. Sci. 10 (1980) 111–121.
It is proved that the 2-DIRECTED DISJOINT PATHS PROBLEM is NP-complete in general digraphs. The proof is pretty concise, but I have some difficulties with figuring the correctness of the given reduction from 3-SAT, mostly due to the old-fashion writing and omitted justification of details.
Does anyone here know a resource, say a textbook, in which a more comprehensible version of this proof (or maybe an alternative one) is presented?
Thanks in advance.