Intersect incident Edges and Nodes

This macro assures, that every node and edge, which are incident, share at least one grid point. To accomplish this we define a new variable xin(rows[1..#rows-2], cols[1..#cols-2], nodes, edges). The new variable is one iff an edge e and a node n share the grid point (r,c). For each edge e and its source and target nodes, the sum over all grid points has to be at least 1.
This makro uses the following other makros:
   • defaultvariables_objects.gdsl