diff --git a/src/main/java/puzzle/SwedishGenerator.java b/src/main/java/puzzle/SwedishGenerator.java
index 1ffbf09..8b21a6c 100644
--- a/src/main/java/puzzle/SwedishGenerator.java
+++ b/src/main/java/puzzle/SwedishGenerator.java
@@ -289,8 +289,8 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
          return lisLetterAtHi(pos);
       }
       
-      public boolean lisLetterAtLo(int pos) { return (lo & (1L << pos)) != 0; }
-      public boolean lisLetterAtHi(int pos) { return (hi & (1L << (pos & 63))) != 0; }
+      public boolean lisLetterAtLo(int pos) { return (lo & (1L << pos)) != X; }
+      public boolean lisLetterAtHi(int pos) { return (hi & (1L << (pos & 63))) != X; }
       void setLetterLo(int idx, byte ch) {
          lo |= (1L << idx);
          
@@ -411,11 +411,11 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
       
       if (Slot.increasing(key)) {
          // first clue is lowest index among hits (lo first, then hi)
-         if (hitsLo != 0) {
+         if (hitsLo != X) {
             long stop = 1L << Long.numberOfTrailingZeros(hitsLo);
             rayLo &= (stop - 1);
             rayHi = 0; // any hi is beyond the stop
-         } else if (hitsHi != 0) {
+         } else if (hitsHi != X) {
             long stop = 1L << Long.numberOfTrailingZeros(hitsHi);
             // keep all lo (lo indices are < any hi index), but cut hi below stop
             rayHi &= (stop - 1);
@@ -471,7 +471,7 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
                if (hLo != X) {
                   rLo &= ((1L << Long.numberOfTrailingZeros(hLo)) - 1);
                   rHi = 0;
-               } else if (hHi != 0) { rHi &= ((1L << Long.numberOfTrailingZeros(hHi)) - 1); }
+               } else if (hHi != X) { rHi &= ((1L << Long.numberOfTrailingZeros(hHi)) - 1); }
             } else {
                if (hHi != X) {
                   int msb = 63 - Long.numberOfLeadingZeros(hHi);
@@ -563,8 +563,8 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
          int clueIdx = Long.numberOfTrailingZeros(bits);
          var rci     = IT[clueIdx];
          if ((4 - rci.nbrCount()) + Long.bitCount(rci.n1() & lo_cl) + Long.bitCount(rci.n2() & hi_cl) >= 3) penalty += 400;
-         boolean h = (cHLo & (1L << clueIdx)) != 0;
-         boolean v = (cVLo & (1L << clueIdx)) != 0;
+         boolean h = (cHLo & (1L << clueIdx)) != X;
+         boolean v = (cVLo & (1L << clueIdx)) != X;
          if (!h && !v) penalty += 1500;
          else if (h && v) { /* ok */ } else if (h | v) penalty += 200;
          else penalty += 600;
@@ -573,8 +573,8 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
          int clueIdx = Long.numberOfTrailingZeros(bits);
          var rci     = IT[64 | clueIdx];
          if ((4 - rci.nbrCount()) + Long.bitCount(rci.n1() & lo_cl) + Long.bitCount(rci.n2() & hi_cl) >= 3) penalty += 400;
-         boolean h = (cHHi & (1L << clueIdx)) != 0;
-         boolean v = (cVHi & (1L << clueIdx)) != 0;
+         boolean h = (cHHi & (1L << clueIdx)) != X;
+         boolean v = (cVHi & (1L << clueIdx)) != X;
          if (!h && !v) penalty += 1500;
          else if (h && v) { /* ok */ } else if (h | v) penalty += 200;
          else penalty += 600;
@@ -772,7 +772,7 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
    static boolean placeWord(Grid grid, final int key, final long lo, final long hi, final long w) {
       final long glo = grid.lo, ghi = grid.hi;
       if (Slot.increasing(key)) {
-         for (long b = lo & glo; b != 0; b &= b - 1) {
+         for (long b = lo & glo; b != X; b &= b - 1) {
             int idx = Long.numberOfTrailingZeros(b);
             if (grid.g[idx] != Lemma.byteAt(w, Long.bitCount(lo & ((1L << idx) - 1)))) return false;
          }
@@ -808,7 +808,7 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
          
          long maskLo = lo & ~glo, maskHi = hi & ~ghi;
          if ((maskLo | maskHi) != X) {
-            for (long b = maskHi; b != 0; b &= b - 1) {
+            for (long b = maskHi; b != X; b &= b - 1) {
                int idx = Long.numberOfTrailingZeros(b);
                grid.g[64 | idx] = Lemma.byteAt(w, Long.bitCount(hi & ~((1L << idx) | ((1L << idx) - 1))));
             }
@@ -828,7 +828,7 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
       
       for (long p = pattern; p != X; ) {
          int combined = (int) (p & 0xFF);
-         if (combined != 0) {
+         if (combined != X) {
             long[] bs = posBitsets[combined - 1];
             if (first) {
                System.arraycopy(bs, 0, res, 0, numLongs);
@@ -864,7 +864,7 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
       
       for (long p = pattern; p != X; ) {
          int combined = (int) (p & 0xFF);
-         if (combined != 0) {
+         if (combined != X) {
             long[] bs = posBitsets[combined - 1];
             if (first) {
                System.arraycopy(bs, 0, res, 0, numLongs);