diff --git a/Makefile b/Makefile
index e718ff6..462b2da 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 HEADERS=coxeter.h thickenings.h queue.h
-OPTIONS=-O3 -g -std=gnu99
+OPTIONS=-O3 -std=gnu99
 
 all: generate process test
 
diff --git a/coxeter.c b/coxeter.c
index 122f7b3..1fc78aa 100644
--- a/coxeter.c
+++ b/coxeter.c
@@ -70,6 +70,14 @@ static void generate_schlaefli_matrix(semisimple_type_t type, gsl_matrix *mat)
 	    gsl_matrix_set(mat, offset + i, offset + j, 2.0);
 	  else if(i > 0 && j > 0 && (i - j == 1 || i - j == -1) || i == 0 && j == 2 || i == 2 && j == 0)
 	    gsl_matrix_set(mat, offset + i, offset + j, -1.0);
+    } else if(type.factors[k].series == 'F') {
+      ERROR(type.factors[k].rank != 4, "A Coxeter group of type %c%d does not exist or is not implemented!\n", type.factors[k].series, type.factors[k].rank);
+      for(int i = 0; i < 4; i++)
+	gsl_matrix_set(mat, offset + i, offset + i, 2.0);
+      for(int i = 0; i < 3; i++) {
+	gsl_matrix_set(mat, offset + i, offset + i + 1, i == 1 ? -sqrt(2.0) : -1.0);
+	gsl_matrix_set(mat, offset + i + 1, offset + i, i == 1 ? -sqrt(2.0) : -1.0);
+      }
     } else if(type.factors[k].series == 'G') {
       ERROR(type.factors[k].rank != 2, "A Coxeter group of type %c%d does not exist or is not implemented!\n", type.factors[k].series, type.factors[k].rank);
       gsl_matrix_set(mat, offset + 0, offset + 0, 2.0);
diff --git a/process.c b/process.c
index f548f44..c62cad2 100644
--- a/process.c
+++ b/process.c
@@ -51,7 +51,8 @@ int main(int argc, const char *argv[])
   signed char *level;
   node_t *graph;
   int *left, *right;
-  int *left_invariant, *right_invariant;
+  int left_invariant, right_invariant;
+  int left_invariant_wanted = 0, right_invariant_wanted = 0;
   edgelist_t *edgelists;
   int *words;
 
@@ -59,7 +60,7 @@ int main(int argc, const char *argv[])
   int current;
   int *seen;
   int *generators;
-  int ngens, nleft, nright;
+  int ngens;
 
   char string_buffer1[1000];
   const char *alphabet = "abcdefghijklmnopqrstuvwxyz";
@@ -68,8 +69,21 @@ int main(int argc, const char *argv[])
 
   if(argc < 2)
     infile = stdin;
-  else
-    infile = fopen(argv[1], "rb");
+  else {
+    if(strcmp(argv[1], "-") == 0)
+      infile = stdin;
+    else
+      infile = fopen(argv[1], "rb");
+
+    if(argc >= 4) {
+      if(strcmp(argv[2], "-") != 0)
+	for(int i = 0; i < strlen(argv[2]); i++)
+	  left_invariant_wanted |= (1 << (argv[2][i] - 'a'));
+      if(strcmp(argv[3], "-") != 0)
+	for(int i = 0; i < strlen(argv[3]); i++)
+	  right_invariant_wanted |= (1 << (argv[3][i] - 'a'));
+    }
+  }
 
   fread(&type.n, sizeof(int), 1, infile);  // we completely trust the input data
   type.factors = malloc(type.n * sizeof(simple_type_t));
@@ -83,8 +97,6 @@ int main(int argc, const char *argv[])
   graph = (node_t*)malloc(order*sizeof(node_t));
   left = (int*)malloc(order*rank*sizeof(int));
   right = (int*)malloc(order*rank*sizeof(int));
-  left_invariant = (int*)malloc(rank*sizeof(int));
-  right_invariant = (int*)malloc(rank*sizeof(int));
   seen = (int*)malloc(order*sizeof(int));
   generators = (int*)malloc(order*sizeof(int));
   level = (signed char*)malloc(order*sizeof(int));
@@ -106,57 +118,46 @@ int main(int argc, const char *argv[])
     continue;
     */
 
-    for(int j = 0; j < rank; j++) {
-      left_invariant[j] = 1;
-      right_invariant[j] = 1;
-    }
+    left_invariant = right_invariant = -1; // all 1s
     for(int j = 0; j < order; j++) {
       for(int k = 0; k < rank; k++) {
 	if(level[j] > 0 && level[graph[j].left[k]] < 0 || level[j] < 0 && level[graph[j].left[k]] > 0) {
-	  left_invariant[k] = 0;
+	  left_invariant &= ~(1 << k);
 	}
 	if(level[j] > 0 && level[graph[j].right[k]] < 0 || level[j] < 0 && level[graph[j].right[k]] > 0) {
-	  right_invariant[k] = 0;
+	  right_invariant &= ~(1 << k);
 	}
       }
     }
 
-    nleft = nright = 0;
-    for(int j = 0; j < rank; j ++) {
-      if(left_invariant[j])
-	nleft++;
-      if(right_invariant[j])
-	nright++;
-    }
-
-    ngens = 0;
-    memset(generators, 0, order*sizeof(int));
-    for(int j = 0; j < order; j++) {
-      if(level[j] == HEAD_MARKER && generators[j] == 0) { // ignore the generator, if it is equivalent to one already seen
-	ngens++;
-	queue_init(&queue);
-	queue_put(&queue, j);
-	while((current = queue_get(&queue)) != -1) {
-	  if(generators[current] == 0) { // visit everyone only once
-	    generators[current] = ngens;
-	    for(int k = 0; k < rank; k++) {
-	      if(left_invariant[k])
+    if((~left_invariant & left_invariant_wanted) == 0 && (~right_invariant & right_invariant_wanted) == 0) {
+      ngens = 0;
+      memset(generators, 0, order*sizeof(int));
+      for(int j = 0; j < order; j++) {
+	if(level[j] == HEAD_MARKER && generators[j] == 0) { // ignore the generator, if it is equivalent to one already seen
+	  ngens++;
+	  queue_init(&queue);
+	  queue_put(&queue, j);
+	  while((current = queue_get(&queue)) != -1) {
+	    if(generators[current] == 0) { // visit everyone only once
+	      generators[current] = ngens;
+	      for(int k = 0; k < rank; k++) {
+		if(left_invariant & (1 << k))
 		queue_put(&queue, graph[current].left[k]);
-	      if(right_invariant[k])
-		queue_put(&queue, graph[current].right[k]);
+		if(right_invariant & (1 << k))
+		  queue_put(&queue, graph[current].right[k]);
+	      }
 	    }
 	  }
 	}
       }
-    }
 
-    if(nleft >= 2 && nright >= 2) {
       printf("left: ");
       for(int j = 0; j < rank; j++)
-	printf("%c", left_invariant[j] ? alphabet[j] : ' ');
+	printf("%c", left_invariant & (1 << j) ? alphabet[j] : ' ');
       printf(" right: ");
       for(int j = 0; j < rank; j++)
-	printf("%c", right_invariant[j] ? alphabet[j] : ' ');
+	printf("%c", right_invariant & (1 << j) ? alphabet[j] : ' ');
       printf(" generators: ");
 
       memset(seen, 0, order*sizeof(int));
@@ -190,8 +191,6 @@ int main(int argc, const char *argv[])
   free(graph);
   free(left);
   free(right);
-  free(right_invariant);
-  free(left_invariant);
   free(seen);
   free(generators);
   free(type.factors);
diff --git a/test.c b/test.c
index 742410c..385ae14 100644
--- a/test.c
+++ b/test.c
@@ -3,6 +3,28 @@
 #include "thickenings.h"
 #include "queue.h"
 
+#define SWAP(t, a, b) do {t tmp = a; a = b; b = tmp;} while(0)
+
+char *stringify_Sp2n_permutation(int *word, int wordlength, int rank, int len, char *str)
+{
+  for(int i = 0; i < rank*2; i++)
+    str[i] = '1' + i;
+  str[2*rank] = 0;
+
+  for(int i = 0; i < wordlength; i++) {
+    if(word[i] == 0)
+      SWAP(char, str[rank-1], str[2*rank-1]);
+    else {
+      SWAP(char, str[rank-word[i]], str[rank-word[i]-1]);
+      SWAP(char, str[2*rank-word[i]], str[2*rank-word[i]-1]);
+    }
+  }
+
+  str[len] = 0;
+
+  return str;
+}
+
 int main(int argc, const char *argv[])
 {
   semisimple_type_t type;
@@ -17,13 +39,13 @@ int main(int argc, const char *argv[])
   char alphabet[] = "abcdefghijklmnopqrstuvwxyz";
   char buffer[1024];
 
-  int left = ~0x01; // 1111 1110
-  int right = ~0x01; // 1111 1101
+  int left = ~(1 << (atoi(argv[1]) - atoi(argv[3])));
+  int right = ~(1 << (atoi(argv[1]) - atoi(argv[2])));
 
   type.n = 1;
   type.factors = (simple_type_t*)malloc(type.n*sizeof(simple_type_t));
   type.factors[0].series = 'B';
-  type.factors[0].rank = 4;
+  type.factors[0].rank = atoi(argv[1]);
 
   rank = coxeter_rank(type);
   order = coxeter_order(type);
@@ -77,9 +99,10 @@ int main(int argc, const char *argv[])
   for(int i = 0; i < order; i++)
     if(reduced[i] == i) {
       if(i == 0)
-	printf("1 ");
+      	printf("1 ");
       else
 	printf("%s ", alphabetize(graph[i].word, graph[i].wordlength, alphabet, buffer));
+      //      printf("%s ", stringify_Sp2n_permutation(graph[i].word, graph[i].wordlength, rank, atoi(argv[2]), buffer));
     }
 
   printf("\n");
diff --git a/thickenings.c b/thickenings.c
index 71fee42..9d72f56 100644
--- a/thickenings.c
+++ b/thickenings.c
@@ -375,9 +375,9 @@ void enumerate_balanced_thickenings(semisimple_type_t type, node_t *graph, const
 
       if(is_fat) {
 	//      ERROR(count >= MAX_THICKENINGS, "Too many balanced thickenings! Increase MAX_THICKENINGS\n");
-	if(count % 10000000 == 0)
-	  print_thickening(rank, order, level, 0, 0, 0, alphabet, stderr);
-	//	fwrite(level, sizeof(signed char), order, outfile);
+	//if(count % 10000000 == 0)
+	//print_thickening(rank, order, level, 0, 0, 0, alphabet, stderr);
+	fwrite(level, sizeof(signed char), order, outfile);
 	count++;
       }
     }