--- a/nono.py	Sun Mar 22 18:15:42 2020 +0000
+++ b/nono.py	Tue Mar 24 18:57:33 2020 +0000
@@ -108,13 +108,17 @@
           dprint('s2',i-1,j)
           if j is not None:
             # Only if we actually added a blob at some point
+            dpush('b_s2')
             self.checkNew(i-1)
+            dpop('b_s2')
       elif self[i].val is True and maybeSeq is None:
         dprint('s3',i)
         maybeSeq=i
     dprint('s4',inSeq,i)
     if inSeq is not None:
+      dpush('b_s4')
       self.checkNew(i)
+      dpop('b_s4')
     return changed
 
   def onepass(self,i0,iBound,scratch,stack):
@@ -266,18 +270,19 @@
       self.resetAllRuns()
 
   def marginal(self,rng,l):
-    dprint('m',rng.start,rng.stop,rng.step)
+    dprint('m%s'%self.cLet,rng.start,rng.stop,rng.step,l)
     g=0 # length of a gap
     for i in rng:
       if self[i].val is True:
-        # Should//n't be possible?
+        # Shouldn't be possible?
         dprint('mx0')
         return False
       if self[i].val is False:
         if g>0:
           # Block a too-small gap
-          for i in (i-g,i):
-            self.newX(i,True)
+          dprint('m1',i-g,i)
+          for j in range(i-g,i):
+            self.newX(j,True)
           g=0
       else:
         # None
@@ -288,7 +293,8 @@
           return False
     if g>0:
       # Block a too-small gap
-      for j in (i-g,i):
+      dprint('m2',i-g,i)
+      for j in range(i+1-g,i+1):
         self.newX(j,True)
     return True
 
@@ -347,13 +353,17 @@
   def newBlob(self,x,crossCheck=False):
     self[x].setVal(True)
     if crossCheck:
+      dpush('b_cc')
       self[x].column.checkNew(self.y)
+      dpop('b_cc')
 
   def newX(self,x,crossCheck=False):
     dprint('nx %s%s@%s'%('R',self.y,x))
     self[x].setVal(False)
     if crossCheck:
+      dpush('x_cc')
       self[x].column.checkX(self.y,x)
+      dpop('x_cc')
 
 class Column(Vector):
   cLet='C'
@@ -396,13 +406,17 @@
   def newBlob(self,y,crossCheck=False):
     self[y].setVal(True)
     if crossCheck:
+      dpush('b_cc')
       self[y].row.checkNew(self.x)
+      dpop('b_cc')
 
   def newX(self,y,crossCheck=False):
     dprint('nx %s%s@%s'%('C',self.x,y))
     self[y].setVal(False)
     if crossCheck:
+      dpush('x_cc')
       self[y].row.checkX(self.x,y)
+      dpop('x_cc')
 
 class Cell:
   def __init__(self,row,y,column,x):
@@ -438,7 +452,11 @@
 class Nono(dict):
   # 0,0 is upper left, so increasing y goes _downwards_, to match the standard layout
   def __init__(self,runsPerRow,runsPerCol):
+    global SOLVER
     self.loop=0
+    self.dp=''
+    self.dstate=[]
+    SOLVER=self
     n=self.n=len(runsPerCol)
     if n!=len(runsPerRow):
       print("losing r:%s x c:%s"%(len(runsPerRow),n),sys.stderr)
@@ -481,7 +499,16 @@
       print(someChanged)
       print(self)
 
+def dpush(s):
+  SOLVER.dp+=' '
+  SOLVER.dstate.append(s)
+
+def dpop(s):
+  assert(SOLVER.dstate.pop()==s)
+  SOLVER.dp=SOLVER.dp[1:]
+
 def dprint(*args):
+  print(SOLVER.dp,end='')
   print(*args)
   sys.stdout.flush()