Update 2sat.h

Author: simonlindholm

content/graph/2sat.h

@@ -1,7 +1,8 @@
 /**
  * Author: Emil Lenngren, Simon Lindholm
  * Date: 2011-11-29
- * Source:
+ * License: CC0
+ * Source: folklore
  * Description: Calculates a valid assignment to boolean variables a, b, c,... to a 2-SAT problem, so that an expression of the type $(a\|\|b)\&\&(!a\|\|c)\&\&(d\|\|!b)\&\&...$ becomes true, or reports that it is unsatisfiable.
  * Negated variables are represented by bit-inversions (\texttt{\tilde{}x}).
  * Usage: