diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a803088
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+extended/*
diff --git a/gen_eq_instances.py b/gen_eq_instances.py
new file mode 100755
index 0000000..865620f
--- /dev/null
+++ b/gen_eq_instances.py
@@ -0,0 +1,117 @@
+#!python3
+
+from pysat.formula import CNF
+from pysat.solvers import Glucose4
+
+import pathlib as pl
+import random
+import bz2
+import sys
+
+CORE_DIR = pl.Path("./cores")
+EXTENDED_DIR = pl.Path("./extended")
+
+usage_str = "usage: gen_eq_instance.py [instance dir] [num per instance]"
+
+def main():
+    instances_dir = None
+
+    try:
+        instances_dir = pl.Path(sys.argv[1])
+    except:
+        print(usage_str)
+        return
+    else:
+        if not instances_dir.is_dir():
+            print(usage_str)
+            return
+
+    num_per_instance = 0
+    try:
+        num_per_instance = int(sys.argv[2])
+    except:
+        print(usage_str)
+        return
+
+
+    instances = get_instance_paths(instances_dir)
+    
+    for instance in instances:
+        run(instance, num_per_instance)
+
+def get_instance_paths(instances_dir):
+    instances = []
+
+    for p in instances_dir.iterdir():
+        if str(p).endswith(".cnf.bz2"):
+            instances.append(p)
+
+    return instances 
+
+def run(instance, calls_per_instance):
+    ipath = pl.Path(instance)
+    iname = ipath.stem[:-4]
+
+    f = CNF(str(ipath))
+    
+    for i in range(calls_per_instance):
+        extension = gen_extension(iname, len(f.clauses) / 10)
+        
+        #tmp_f = f.copy()
+        #tmp_f.extend(extension)
+        
+        ext_f = CNF()
+        ext_f.extend(extension)
+
+        print(iname)
+        print(len(f.clauses))
+        print()
+
+        ext_f.to_file(next_file_path(iname),
+                      comments=["c {} core extended".format(iname),
+                                "c number of cores: {}".format(len(extension))],
+                      compress_with="bzip2")
+
+def gen_extension(instance, expected_num_of_core):
+    cores = parse_cores(instance)
+
+    p = expected_num_of_core / len(cores)
+    
+    extension = []
+    
+    print((expected_num_of_core * 10) / len(cores))
+    print(expected_num_of_core * 10, len(cores))
+
+    for core in cores:
+        if p >= random.random():
+            extension.append(core)
+
+    return extension
+
+def parse_cores(instance):
+    cores = []
+    
+    with bz2.open(CORE_DIR / (instance + ".cores.bz2"), "tr") as cores_file:
+        cores = list(map(lambda l: l.strip(), cores_file.readlines()))
+    
+    cores = list(map(lambda l: l.split(","), cores))
+    
+    for i in range(len(cores)):
+        cores[i] = list(map(int, cores[i]))
+        cores[i] = list(map(lambda lit: -1 * lit, cores[i]))
+
+    return cores
+
+def next_file_path(name):
+    counter = 0
+
+    ext_file_path = EXTENDED_DIR / ("{}_{:04}.cnf.bz2".format(name, counter))
+
+    while ext_file_path.exists():
+        counter += 1
+        ext_file_path = EXTENDED_DIR / ("{}_{:04}.cnf.bz2".format(name, counter))
+        
+    return ext_file_path 
+
+if __name__ == "__main__":
+    main()