diff --git a/fcore/bin-search.sml b/fcore/bin-search.sml
index 6c878c3..3b576e7 100644
--- a/fcore/bin-search.sml
+++ b/fcore/bin-search.sml
@@ -69,4 +69,28 @@ struct
     fun equalOrMore (findNum, vec) =
       helpBinSearch (findNum, vec, 0, Vector.length vec - 1)
   end
+
+  local
+    fun helpExists (findNum, vec, low, high) =
+      let
+        val mid = low + ((high - low) div 2)
+      in
+        if high >= low then
+          let
+            val midVal = Vector.sub (vec, mid)
+          in
+            if midVal = findNum then
+              true
+            else if midVal < findNum then
+              helpExists (findNum, vec, mid + 1, high)
+            else
+              helpExists (findNum, vec, low, mid - 1)
+          end
+        else
+          false
+      end
+  in
+    fun exists (findNum, vec) =
+      helpExists (findNum, vec, 0, Vector.length vec - 1)
+  end
 end
diff --git a/fcore/build-search-list.sml b/fcore/build-search-list.sml
index 7debfd1..fef9892 100644
--- a/fcore/build-search-list.sml
+++ b/fcore/build-search-list.sml
@@ -5,8 +5,7 @@ struct
       case tl of
         tlhd :: tltl =>
           helpNextMatch (0, tlhd, tltl, absIdx, searchString, matchedChrs)
-      | [] => 
-          NONE
+      | [] => NONE
     else
       let
         val hdChr = String.sub (hd, idx)
@@ -14,13 +13,11 @@ struct
       in
         if hdChr = searchChr then
           if matchedChrs + 1 = String.size searchString then
-            let
-              val matchedIdx = absIdx - String.size searchString + 1
-            in
-              SOME matchedIdx
+            let val matchedIdx = absIdx - String.size searchString + 1
+            in SOME matchedIdx
             end
           else
-            helpNextMatch 
+            helpNextMatch
               (idx + 1, hd, tl, absIdx + 1, searchString, matchedChrs + 1)
         else
           helpNextMatch (idx + 1, hd, tl, absIdx + 1, searchString, 0)
@@ -29,20 +26,18 @@ struct
   fun nextMatch (bufferIdx, absIdx, rightStrings, searchString) =
     case rightStrings of
       hd :: tl =>
-        let 
+        let
           val strIdx = absIdx - bufferIdx
         in
           if strIdx < String.size hd then
             helpNextMatch (strIdx, hd, tl, absIdx, searchString, 0)
           else
             (case tl of
-              tlhd :: tltl =>
-                let
-                  val strIdx = strIdx - String.size hd
-                in
-                  helpNextMatch (strIdx, tlhd, tltl, absIdx, searchString, 0)
-                end
-            | [] => NONE)
+               tlhd :: tltl =>
+                 let val strIdx = strIdx - String.size hd
+                 in helpNextMatch (strIdx, tlhd, tltl, absIdx, searchString, 0)
+                 end
+             | [] => NONE)
         end
     | [] => NONE
 
@@ -53,12 +48,26 @@ struct
     in
       case nextMatch (bufferIdx, absIdx, rightStrings, searchString) of
         SOME matchedIdx =>
-          let
-            val searchList = SearchList.append (matchedIdx, searchList)
-          in
+          (* Edge case: we may be searching for a string like "a"
+           * when the buffer represents "aaa aaa aaa".
+           * In this case, there will be continual matches that are consecutive
+           * and we need to check every char in the buffer which is absIdx + 1.
+           * However, we can skip to matchedIdx + 1 if matchedIdx already exists
+           * in the searchList because we know the string between
+           * [absIdx ... matchedIdx - 1] contains no matches.
+           * This check is important to preserve the set-like semaantics
+           * of the searchList too: SearchList.append does not check for this.
+           * *)
+          if SearchList.exists (matchedIdx, searchList) then
             helpFromStart
               (app, origIdx, matchedIdx + 1, buffer, searchString, searchList)
-          end
+          else
+            let
+              val searchList = SearchList.append (matchedIdx, searchList)
+            in
+              helpFromStart
+                (app, origIdx, absIdx + 1, buffer, searchString, searchList)
+            end
       | NONE =>
           let
             val buffer = LineGap.goToIdx (origIdx, buffer)
@@ -80,38 +89,46 @@ struct
       app
 
   (* searches for matchedIdx within a range from the buffer instead of from start *)
-  fun helpFromRange 
+  fun helpFromRange
     (origIdx, curIdx, finishIdx, buffer, searchString, searchList) =
-      let
-        val buffer = LineGap.goToIdx (curIdx, buffer) 
-        val {idx = bufferIdx, rightStrings, ...} = buffer 
-      in
-        case nextMatch (bufferIdx, curIdx, rightStrings, searchString) of
-          SOME matchedIdx =>
-            if matchedIdx > finishIdx then
-              let
-                val buffer = LineGap.goToIdx (origIdx, buffer)
-                val searchList = SearchList.goToNum (origIdx, searchList)
-              in
-                (buffer, searchList)
-              end
-            else
-              let
-                val searchList = SearchList.insert (matchedIdx, searchList)
-              in
-                helpFromRange
-                  ( origIdx, matchedIdx + 1, finishIdx
-                  , buffer, searchString, searchList
-                  )
-              end
-        | NONE =>
+    let
+      val buffer = LineGap.goToIdx (curIdx, buffer)
+      val {idx = bufferIdx, rightStrings, ...} = buffer
+    in
+      case nextMatch (bufferIdx, curIdx, rightStrings, searchString) of
+        SOME matchedIdx =>
+          if matchedIdx > finishIdx then
             let
               val buffer = LineGap.goToIdx (origIdx, buffer)
               val searchList = SearchList.goToNum (origIdx, searchList)
             in
               (buffer, searchList)
             end
-      end
+          else
+            let
+              val searchList = 
+                if SearchList.exists (matchedIdx, searchList) then
+                  searchList
+                else
+                  SearchList.insert (matchedIdx, searchList)
+            in
+              helpFromRange
+                ( origIdx
+                , curIdx + 1
+                , finishIdx
+                , buffer
+                , searchString
+                , searchList
+                )
+            end
+      | NONE =>
+          let
+            val buffer = LineGap.goToIdx (origIdx, buffer)
+            val searchList = SearchList.goToNum (origIdx, searchList)
+          in
+            (buffer, searchList)
+          end
+    end
 
   fun fromRange (startIdx, length, buffer, searchString, searchList) =
     let
diff --git a/fcore/search-list.sml b/fcore/search-list.sml
index 420ba3c..8111ccb 100644
--- a/fcore/search-list.sml
+++ b/fcore/search-list.sml
@@ -3,6 +3,7 @@ sig
   type t = {left: int vector list, right: int vector list}
   val empty: t
 
+  val exists: int * t -> bool
   val insert: int * t -> t
   val append: int * t -> t
   val delete: int * int * string * t -> t
@@ -587,4 +588,38 @@ struct
     in
       moveRightAndMap (num, mapBy, left, right)
     end
+
+  fun helpExistsRight (num, right) =
+    case right of
+      hd :: tl =>
+        let
+          val rlast = Vector.sub (hd, Vector.length hd - 1)
+        in
+          if num > rlast then helpExistsRight (num, tl)
+          else BinSearch.exists (num, hd)
+        end
+    | [] => false
+
+  fun helpExistsLeft (num, left) =
+    case left of
+      hd :: tl =>
+        let
+          val lfirst = Vector.sub (hd, 0)
+        in
+          if num < lfirst then helpExistsLeft (num, tl)
+          else BinSearch.exists (num, hd)
+        end
+    | [] => false
+
+  fun exists (num, {left, right}) =
+    case right of
+      rhd :: rtl =>
+        let
+          val rfirst = Vector.sub (rhd, 0)
+        in
+          if num = rfirst then true
+          else if num > rfirst then helpExistsRight (num, right)
+          else helpExistsLeft (num, left)
+        end
+    | [] => helpExistsLeft (num, left)
 end