diff --git a/src/claims.c b/src/claims.c
new file mode 100644
index 0000000..62a387a
--- /dev/null
+++ b/src/claims.c
@@ -0,0 +1,193 @@
+#include <stdlib.h>
+#include "termmaps.h"
+#include "runs.h"
+#include "error.h"
+
+#define MATCH_NONE 0
+#define MATCH_ORDER 1
+#define MATCH_REVERSE 2
+
+#define LABEL_GOOD -3
+#define LABEL_TODO -2
+
+/*
+ * Validity checks for claims
+ */
+
+//! Check complete message match
+/**
+ *@returns any of the MATCH_ signals
+ */
+int
+events_match (const System sys, const int i, const int j)
+{
+  Roledef rdi, rdj;
+
+  rdi = sys->traceEvent[i];
+  rdj = sys->traceEvent[j];
+  if (rdi->message == rdj->message && rdi->from == rdj->from &&
+      rdi->to == rdj->to && rdi->label == rdj->label &&
+      !(rdi->internal || rdj->internal))
+    {
+      if (rdi->type == SEND && rdj->type == READ)
+	{
+	  if (i<j)
+	      return MATCH_ORDER;
+	  else
+	      return MATCH_REVERSE;
+	}
+      if (rdi->type == READ && rdj->type == SEND)
+	{
+	  if (i>j)
+	      return MATCH_ORDER;
+	  else
+	      return MATCH_REVERSE;
+	}
+    }
+  return MATCH_NONE;
+}
+
+//! nisynch generalization
+/**
+ * f maps the involved roles to run identifiers.
+ * g maps all labels in prec to the event indices for things already found,
+ * or to LABEL_TODO for things not found yet but in prec, and LABEL_GOOD for well linked messages (and that have thus defined a runid for the corresponding role).
+ * All values not in prec map to -1.
+ */
+int
+oki_nisynch (const System sys, const int i, const Termmap f, const Termmap g)
+{
+  // Check for completed trace
+  if (i == -1)
+    {
+      // Are all labels well linked?
+      Termmap gscan;
+
+      gscan = g;
+      while (gscan != NULL)
+	{
+	  if (gscan->result != LABEL_GOOD)
+	      return 0;
+	  gscan = gscan->next;
+	}
+      return 1;
+    }
+  else
+    {
+      Roledef rd;
+      int rid;
+
+      rd = sys->traceEvent[i];
+      rid = sys->traceRun[i];
+      /*
+       * Simple case: internal event or claim
+       */
+      if (rd->type == CLAIM || rd->internal)
+	{
+	  return oki_nisynch (sys,i-1,f,g);
+	}
+      else
+	{
+	  /*
+	   * More difficult cases: send and read
+	   */
+	  if (rd->type == READ)
+	    {
+	      /*
+	       * Read is only relevant for already involved runs, and labels in prec
+	       */
+              Termmap fscan;
+
+	      fscan = f;
+	      while (fscan != NULL)
+		{
+		  if (fscan->result == rid)
+		    {
+		      // Involved, but is it a prec label?
+		      if (termmapGet (g, rd->label) == LABEL_TODO)
+			{
+			  Termmap gbuf;
+			  int result;
+
+			  gbuf = termmapDuplicate (g);
+			  gbuf = termmapSet (gbuf, rd->label, i);
+			  result = oki_nisynch (sys,i-1,f,gbuf);
+			  termmapDelete (gbuf);
+			  return result;
+		        }
+		    }
+		  fscan = fscan->next;
+		}
+	      // Apparently not involved
+	      return oki_nisynch (sys,i-1,f,g);
+	    }
+	  if (rd->type == SEND)
+	    {
+	      // Scan whether we were waiting for it or not
+	      int result;
+	      int rid2;
+	      Term rolename;
+	      Termmap gscan;
+
+	      rolename = sys->runs[rid].role->nameterm;
+	      rid2 = termmapGet (f, rolename);
+	      result = oki_nisynch (sys, i-1, f, g);
+	      // Assume that this run is not yet involved 
+	      gscan = g;
+	      while (gscan != NULL)
+		{
+		  // Ordered match needed
+		  if (gscan->result > -1 && 
+		      events_match (sys, gscan->result, i) == 1)
+		    {
+		      // Events match: but is the run a good candidate?
+		      if (rid2 == -1 || rid2 == rid)
+			{
+			  Termmap fbuf, gbuf;
+
+			  /**
+			   *@todo Optimization can be done when rid2 == rid, no copy of f needs to be made.
+			   */
+			  fbuf = termmapDuplicate (f);
+			  fbuf = termmapSet (fbuf, rolename, rid);
+			  gbuf = termmapDuplicate (g);
+			  gbuf = termmapSet (gbuf, rd->label, -3);
+			  result = oki_nisynch (sys, i-1, fbuf, gbuf);
+			  termmapDelete (gbuf);
+			  termmapDelete (fbuf);
+			}
+		    }
+		  gscan = gscan->next;
+		}
+	      return result;
+	    }
+	  /*
+	   * Exception: no send, no read, what is it?
+	   */
+	  error ("Unrecognized event type in claim scanner at %i.", i);
+	}
+    }
+}
+
+/*
+ * Real checks
+ */
+
+//! Check validity of ni-synch claim at event i.
+int
+check_claim_nisynch (const System sys, const int i)
+{
+  int result;
+  int rid;
+  Termmap f,g;
+
+  rid = sys->traceRun[i];
+  f = termmapSet (NULL, sys->runs[rid].role->nameterm, rid);
+  /**
+   *@todo g should map all labels in prec to LABEL_TODO
+   */
+  result = oki_nisynch(sys, i, f, NULL);
+  termmapDelete (f);
+  return result;
+}
+
diff --git a/src/claims.h b/src/claims.h
new file mode 100644
index 0000000..3fe7103
--- /dev/null
+++ b/src/claims.h
@@ -0,0 +1,6 @@
+#ifndef CLAIMS
+#define CLAIMS
+
+int check_claim_nisynch (const System sys, const int i);
+
+#endif