diff --git a/src/base/abci/abc.c b/src/base/abci/abc.c
index 1d97f5e415..5c97b3dc4a 100644
--- a/src/base/abci/abc.c
+++ b/src/base/abci/abc.c
@@ -35199,7 +35199,7 @@ int Abc_CommandAbc9Extract( Abc_Frame_t * pAbc, int argc, char ** argv )
     Abc_Print( -2, "usage: &extract [-K <num>] [-vh]\n");
     Abc_Print( -2, "\t           extract shared logic for XOR-rich circuits\n");
     Abc_Print( -2, "\t-K <num> : the minimum gate size to consider for extraction [default = %d]\n", nMultiSize );
-    Abc_Print( -2, "\t-a       : toogle extracting ANDs instead of XORs [default = %s]\n", fAnds? "yes": "no" );
+    Abc_Print( -2, "\t-a       : toggle extracting ANDs instead of XORs [default = %s]\n", fAnds? "yes": "no" );
     Abc_Print( -2, "\t-v       : print verbose information [default = %s]\n", fVerbose? "yes": "no" );
     Abc_Print( -2, "\t-h       : print the command usage\n");
     return 1;
@@ -49492,7 +49492,7 @@ int Abc_CommandAbc9Cfs( Abc_Frame_t * pAbc, int argc, char ** argv )
     Abc_Print( -2, "usage: &cfs [-LNURPrcdvh]\n" );
     Abc_Print( -2, "\t          performs simulation\n" );
     Abc_Print( -2, "\t-L num  : the limit on the number of occurrences [default = %d]\n",  Limit );
-    Abc_Print( -2, "\t-N num  : the number of repetions of each pattern [default = %d]\n", Reps );
+    Abc_Print( -2, "\t-N num  : the number of repetitions of each pattern [default = %d]\n", Reps );
     Abc_Print( -2, "\t-U num  : what to do with unseen patterns [default = %d]\n",         UnseenUse );
     Abc_Print( -2, "\t-R num  : what to do with rare patterns [default = %d]\n",           RareUse );
     Abc_Print( -2, "\t-P num  : base2-log of ramdom flip probability [default = %f]\n",    FlipProb );
diff --git a/src/bdd/cudd/cuddDecomp.c b/src/bdd/cudd/cuddDecomp.c
index 1d534670ca..a20cf5ef68 100644
--- a/src/bdd/cudd/cuddDecomp.c
+++ b/src/bdd/cudd/cuddDecomp.c
@@ -1673,7 +1673,7 @@ ZeroCase(
   constant. At the decomposition point, the factors returned are (f,
   1). Recur on the two children. The order is determined by the
   heavier branch. Combine the factors of the two children and pick the
-  one that already occurs in the gh table. Occurence in g is indicated
+  one that already occurs in the gh table. Occurrence in g is indicated
   by value 1, occurence in h by 2, occurence in both 3.]
 
   SideEffects []
diff --git a/src/opt/rwr/rwrExp.c b/src/opt/rwr/rwrExp.c
index 9d8455b49d..0f716b5f02 100644
--- a/src/opt/rwr/rwrExp.c
+++ b/src/opt/rwr/rwrExp.c
@@ -136,11 +136,11 @@ void Rwt_Man4ExplorePrint()
         pReprs[ s_pManRwrExp4->pnCounts[i] ] = i;
     }
 
-    printf( "Occurence = %6d.  Num classes = %4d.  \n", 0, 2288-nClasses );
+    printf( "Occurrence = %6d.  Num classes = %4d.  \n", 0, 2288-nClasses );
     for ( i = 1; i <= CountMax; i++ )
         if ( pDistrib[i] )
         {
-            printf( "Occurence = %6d.  Num classes = %4d.  Repr = ", i, pDistrib[i] );
+            printf( "Occurrence = %6d.  Num classes = %4d.  Repr = ", i, pDistrib[i] );
             Extra_PrintBinary( stdout, (unsigned*)&(pReprs[i]), 16 ); 
             printf( "\n" );
         }
@@ -256,7 +256,7 @@ void Rwt_Man5ExplorePrint()
     for ( i = 1; i <= CountMax; i++ )
         if ( pDistrib[i] )
         {
-            printf( "Occurence = %6d.  Num classes = %4d.  Repr = ", i, pDistrib[i] );
+            printf( "Occurrence = %6d.  Num classes = %4d.  Repr = ", i, pDistrib[i] );
             Extra_PrintBinary( stdout, pReprs + i, 32 ); 
             printf( "\n" );
         }