A finer reduction of constraint problems to digraphs
  It is well known that the constraint satisfaction problem over a general relational structure A is polynomial time equivalent to the constraint problem over some associated digraph. We present a variant of this construction and show that the corresponding constraint satisfaction problem is logspace equivalent to that over A. Moreover, we show that almost all of the commonly encountered polymorphism properties are held equivalently on the A and the constructed digraph. As a consequence, the Algebraic CSP dichotomy conjecture as well as the conjectures characterizing CSPs solvable in logspace and in nondeterministic logspace are equivalent to their restriction to digraphs. 
Jakub Bul\'in (Charles University, Prague), Dejan Delic (Ryerson   University), Marcel Jackson (La Trobe University), Todd N...
cs.CC cs.LO math.CO