diff --git a/algs4/frequency_counter.py b/algs4/frequency_counter.py
index 60d141d..202a191 100644
--- a/algs4/frequency_counter.py
+++ b/algs4/frequency_counter.py
@@ -1,6 +1,6 @@
 """
     Execution:
-        python frequency_counter L < input.txt
+        python frequency_counter.py L < input.txt
     Data files:   
         https://algs4.cs.princeton.edu/31elementary/tnyTale.txt
         https://algs4.cs.princeton.edu/31elementary/tale.txt
@@ -12,40 +12,35 @@
     the most frequently occurring word that has length greater than
     a given threshold.
 
-    % python frequency_counter 1 < tinyTale.txt
+    % python frequency_counter.py 1 < tinyTale.txt
     it 10
   
-    % python frequency_counter 8 < tale.txt
+    % python frequency_counter.py 8 < tale.txt
     business 122
   
-    % python frequency_counter 10 < leipzig1M.txt
+    % python frequency_counter.py 10 < leipzig1M.txt
     government 24763
 """
 
-#from algs4.st import ST
+import sys
 from algs4.sequential_search_st import SequentialSearchST
 
+minlen = int(sys.argv[1])
+st = SequentialSearchST()
 
-class FrequencyCounter:
-    pass
+for line in sys.stdin:
+    words = line.split()
+    for word in words:
+        if len(word) < minlen:
+            continue
+        if not st.contains(word):
+            st.put(word, 1)
+        else:
+            st.put(word, st.get(word) + 1)
 
-if __name__ == "__main__":
-    import sys
-    minlen = int(sys.argv[1])
-    st = SequentialSearchST()
-    for line in sys.stdin:
-        words = line.split()
-        for word in words:
-
-            if len(word) < minlen:
-                continue
-            if not st.contains(word):
-                st.put(word, 1)
-            else:
-                st.put(word, st.get(word) + 1)
-    maxstr = ""
-    st.put(maxstr, 0)
-    for word in st.keys():
-        if st.get(word) > st.get(maxstr):
-            maxstr = word
-    print(maxstr, " ", st.get(maxstr))
+maxstr = ""
+st.put(maxstr, 0)
+for word in st.keys():
+    if st.get(word) > st.get(maxstr):
+        maxstr = word
+print(maxstr, " ", st.get(maxstr))
diff --git a/algs4/heap.py b/algs4/heap.py
index 7720cc0..e4e7962 100644
--- a/algs4/heap.py
+++ b/algs4/heap.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python heap < tiny.txt
+% python heap.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python heap < words3.txt
+% python heap.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -52,6 +52,7 @@ def sort(cls, arr):
 
         return arr
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/insertion.py b/algs4/insertion.py
index 243f2ba..5382837 100644
--- a/algs4/insertion.py
+++ b/algs4/insertion.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python insertion < tiny.txt
+% python insertion.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python insertion < words3.txt
+% python insertion.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -37,6 +37,7 @@ def sort(cls, arr):
                 j -= 1
         return arr
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/merge.py b/algs4/merge.py
index 799ea97..317aeb6 100644
--- a/algs4/merge.py
+++ b/algs4/merge.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python merge < tiny.txt
+% python merge.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python merge < words3.txt
+% python merge.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -61,6 +61,7 @@ def mergesort(cls, arr, lo, hi):
     def sort(cls, arr):
         return cls.mergesort(arr, 0, len(arr) - 1)
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/queue.py b/algs4/queue.py
index 98ea357..0536014 100644
--- a/algs4/queue.py
+++ b/algs4/queue.py
@@ -1,10 +1,10 @@
 """
-Execution:    python queue < input.txt
+Execution:    python queue.py < input.txt
 
 % more tobe.txt 
 to be or not to - be - - that - - - is
 
-% python queue < tobe.txt
+% python queue.py < tobe.txt
 to be or not to be (2 left on queue)
 """
 
diff --git a/algs4/quick.py b/algs4/quick.py
index c3e7e29..43325a9 100644
--- a/algs4/quick.py
+++ b/algs4/quick.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python quick < tiny.txt
+% python quick.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python quick < words3.txt
+% python quick.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -55,6 +55,7 @@ def quicksort(cls, arr, lo, hi):
     def sort(cls, arr):
         return cls.quicksort(arr, 0, len(arr) - 1)
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/quick_3way.py b/algs4/quick_3way.py
index b7ba1f6..d7887cb 100644
--- a/algs4/quick_3way.py
+++ b/algs4/quick_3way.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python quick 3-way < tiny.txt
+% python quick_3way.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python quick_3way < words3.txt
+% python quick_3way.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -51,6 +51,7 @@ def quicksort(cls, arr, lo, hi):
     def sort(cls, arr):
         return cls.quicksort(arr, 0, len(arr) - 1)
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/selection.py b/algs4/selection.py
index 2a088c9..3ba0f0b 100644
--- a/algs4/selection.py
+++ b/algs4/selection.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python selection < tiny.txt
+% python selection.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python selection < words3.txt
+% python selection.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -36,6 +36,7 @@ def sort(cls, arr):
             arr[i], arr[minIndex] = arr[minIndex], arr[i]
         return arr
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/shell.py b/algs4/shell.py
index 369287b..c761647 100644
--- a/algs4/shell.py
+++ b/algs4/shell.py
@@ -6,7 +6,7 @@
 
 S O R T E X A M P L E
 
-% python shell < tiny.txt
+% python shell.py < tiny.txt
 
 A E E L M O P R S T X                 [ one string per line ]
 
@@ -17,7 +17,7 @@
 bed bug dad yes zoo ... all bad yet
 
 
-% python shell < words3.txt
+% python shell.py < words3.txt
 
 all bad bed bug dad ... yes yet zoo    [ one string per line ]
 """
@@ -43,6 +43,7 @@ def sort(cls, arr):
             h /= 3
         return arr
 
+
 if __name__ == '__main__':
     import sys
 
diff --git a/algs4/stopwatch.py b/algs4/stopwatch.py
index 319b7d7..bb753a3 100644
--- a/algs4/stopwatch.py
+++ b/algs4/stopwatch.py
@@ -1,8 +1,8 @@
 """
- Execution:    python stopwatch n
+ Execution:    python stopwatch.py n
  utility class to measure the running time (wall clock) of a program.
  
- % python stopwatch 10000000
+ % python stopwatch.py 10000000
 2.108185e+10 3.60 seconds
 2.108185e+10 4.53 seconds
  
@@ -18,6 +18,7 @@ def __init__(self):
     def elapsed_time(self):
         return round(time.time() - self.start, 2)
 
+
 if __name__ == '__main__':
     import sys
     import math