diff --git a/index.html b/index.html
index 81b761b..154feeb 100644
--- a/index.html
+++ b/index.html
@@ -34,7 +34,10 @@ td.visible {
   <button id="btnDown" onclick="btnDown_onClick()">Down</button>
   <button id="btnRight" onclick="btnRight_onClick()">Right</button>
   </section>
-  <button onclick="btnGo_onClick();" id="btnGo">Go</button>
+  <section>
+    <button id="btnStart" onclick="btnStart_onClick();">Start</button>
+    <button id="btnRedraw" onclick="btnRedraw_onClick();">Redraw</button>  
+  </section>
   <script src="main.js"></script>
 </body>
 </html>
diff --git a/main.js b/main.js
index e957054..38a6b9a 100644
--- a/main.js
+++ b/main.js
@@ -1,14 +1,21 @@
 const globals = {
     grid: null,
-    tiles: [],
 };
 
-const btnGo_onClick = () => {
+const btnStart_onClick = () => {
     globals.grid = makeGrid(4, 4, {value: 0, visible: false});
     addRandomTile();
+    // globals.grid = makeDevGrid([ // can't slide down or left
+    //     [0,0,1,0],
+    //     [0,0,0,0],
+    //     [0,0,0,0],
+    //     [3,2,3,0],
+    // ]);
+    redraw(globals.grid);
+}
+
+const btnRedraw_onClick = () => {
     redraw(globals.grid);
-    // drawGrid(globals.grid, document.getElementById('output'));
-    // alert("Go");
 }
 
 const btnUp_onClick = () => {
@@ -71,34 +78,84 @@ const drawGrid = (grid, element) => {
 }
 
 const makeGrid = (numRows, numColumns, initialValue) => {
+    const tiles = [];
     const rows = [];
     for (rowIndex = 0; rowIndex < numRows; rowIndex++) {
         const row = [];
         for (columnIndex = 0; columnIndex < numColumns; columnIndex++) {
             position = {row: rowIndex, column: columnIndex};
             const tile = makeTile(initialValue.value, initialValue.visible, rowIndex, columnIndex);
-            globals.tiles.push(tile);
+            tiles.push(tile);
             row.push(tile);
         }
         rows.push(row);
     }
+    const getTile = (grid, row, column) => {
+        return grid.getTile(row, column);
+    }
     const grid = {
         rows,
         numRows,
         numColumns,
+        tiles,
+        clone: () => {
+            const newGrid = makeGrid(numRows, numColumns, makeTile(0, false, 0, 0));
+            for (let rowIndex = 0; rowIndex < numRows; rowIndex++) {
+                for (let columnIndex = 0; columnIndex < numColumns; columnIndex++) {
+                    const newTile = newGrid.getTile(rowIndex, columnIndex);
+                    const oldTile = grid.getTile(rowIndex, columnIndex);
+                    newTile.originalLocation.column = oldTile.originalLocation.column;
+                    newTile.originalLocation.row = oldTile.originalLocation.row;
+                    newTile.value = oldTile.value;
+                    newTile.visible = oldTile.visible;
+                }
+            }
+            return newGrid;
+        },
+        getColumn: (index) => {
+            let vector = [];
+            for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
+                vector.push(grid.getTile(rowIndex, index));
+            }
+            return vector;
+        },
+        getRow: (index) => {
+            let vector = [];
+            for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
+                vector.push(grid.getTile(index, columnIndex));
+            }
+            return vector;
+        },
         getTile: (row, column) => {
-            return rows[row][column];
+            if (row >= 0 && row < numRows && column >= 0 && column < numColumns) {
+                return rows[row][column];
+            }
+            return null;
         },
         setTile: (row, column, tile) => {
-            rows[row][column] = tile;
+            if (row >= 0 && row < numRows && column >= 0 && column < numColumns) {
+                rows[row][column] = tile;
+            }
         },
         swapTiles: (fromRow, fromColumn, toRow, toColumn) => {
-            fromTile = grid.getTile(fromRow, fromColumn);
-            toTile = grid.getTile(toRow, toColumn);
-            // maybe set previous locations on the tiles
-            grid.setTile(fromRow, fromColumn, toTile);
-            grid.setTile(toRow, toColumn, fromTile);
+            if (
+                    fromRow >= 0 && fromRow < numRows
+                    && fromColumn >= 0 && fromColumn < numColumns
+                    && toRow >= 0 && toRow < numRows
+                    && toColumn >= 0 && toColumn < numColumns) {
+                fromTile = grid.getTile(fromRow, fromColumn);
+                toTile = grid.getTile(toRow, toColumn);
+                // maybe set previous locations on the tiles
+                grid.setTile(fromRow, fromColumn, toTile);
+                grid.setTile(toRow, toColumn, fromTile);
+            }
         },
+        toString: (mapFn = i => i.value) => {
+            return "[[" + mapFn(grid.getTile(0, 0)) + "," + mapFn(grid.getTile(0, 1)) + "," + mapFn(grid.getTile(0, 2)) + "," + mapFn(grid.getTile(0, 3)) + "],\n"
+                 + " [" + mapFn(grid.getTile(1, 0)) + "," + mapFn(grid.getTile(1, 1)) + "," + mapFn(grid.getTile(1, 2)) + "," + mapFn(grid.getTile(1, 3)) + "],\n"
+                 + " [" + mapFn(grid.getTile(2, 0)) + "," + mapFn(grid.getTile(2, 1)) + "," + mapFn(grid.getTile(2, 2)) + "," + mapFn(grid.getTile(2, 3)) + "],\n"
+                 + " [" + mapFn(grid.getTile(3, 0)) + "," + mapFn(grid.getTile(3, 1)) + "," + mapFn(grid.getTile(3, 2)) + "," + mapFn(grid.getTile(3, 3)) + "]]";
+        }
     };
     return grid;
 }
@@ -121,7 +178,7 @@ const makeTile = (value, visible, row, column) => {
 };
 
 const addRandomTile = () => {
-    const hiddenTiles = globals.tiles.filter(tile => !tile.visible);
+    const hiddenTiles = globals.grid.tiles.filter(tile => !tile.visible);
     if (hiddenTiles.length <=0) return;
     const index = Math.floor(Math.random() * hiddenTiles.length);
     const tile = hiddenTiles[index];
@@ -134,148 +191,198 @@ const redraw = (grid) => {
     drawGrid(grid, element);
 }
 
-const slideUp = (grid) => {
+const slide = (fromIndex, toIndex, vector, advance, swap, merge, testForDone) => {
+    // const oldSwap = swap;
+    // swap = (fromIndex, toIndex) => {
+    //     const temp = vector[toIndex];
+    //     vector[toIndex] = vector[fromIndex];
+    //     vector[fromIndex] = temp;
+    //     oldSwap(fromIndex, toIndex);
+    // };
     let didIDoIt = false;
-    for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
-        lastIndex = -1;
-        for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex++;
-                if (lastIndex != rowIndex) {
-                    grid.swapTiles(rowIndex, columnIndex, lastIndex, columnIndex);
-                    didIDoIt = true;
+    let hasMergedPrevious = false;
+    while(!testForDone(fromIndex)) {
+        const fromTile = vector[fromIndex];
+        const toTile = toIndex < vector.length && toIndex >= 0 ? vector[toIndex] : null;
+        if (toTile == null) {
+            // Advance toIndex
+            toIndex = advance(toIndex);
+            hasMergedPrevious = false;
+            continue;
+        }
+        if (fromIndex == toIndex) {
+            // Advance fromIndex
+            fromIndex = advance(fromIndex);
+            hasMergedPrevious = false;
+            continue;
+        }
+        if (!toTile.visible) {
+            if (fromTile.visible) {
+                // need to choose row or column
+                swap(fromIndex, toIndex);
+                // Advance fromIndex
+                fromIndex = advance(fromIndex);
+                hasMergedPrevious = false;
+                didIDoIt = true;
+            } else {
+                // Advance fromIndex
+                fromIndex = advance(fromIndex);
+                hasMergedPrevious = false;
+            }
+        } else {
+            if (fromTile.visible) {
+                if (fromTile.value == toTile.value) {
+                    if (hasMergedPrevious) {
+                        // Advance toIndex
+                        toIndex = advance(toIndex);
+                        hasMergedPrevious = false;
+                        didIDoIt = true;
+                    } else {
+                        // Merge tiles
+                        merge(fromTile, toTile);
+                        // Advance fromIndex
+                        fromIndex = advance(fromIndex);
+                        hasMergedPrevious = true;
+                        didIDoIt = true;
+                    }
+                } else {
+                    // Advance toIndex
+                    toIndex = advance(toIndex);
+                    hasMergedPrevious = false;
                 }
+            } else {
+                fromIndex = advance(fromIndex);
+                hasMergedPrevious = false;
             }
         }
     }
     return didIDoIt;
 }
 
+const slideUp = (grid) => {
+    let didIDoIt = false;
+    const advance = i => i + 1;
+    for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
+        const swap = (from, to) => {
+            grid.swapTiles(from, columnIndex, to, columnIndex);
+            const tempTile = vector[to];
+            vector[to] = vector[from];
+            vector[from] = tempTile;
+        };
+        const merge = (from, to) => {
+            to.value++;
+            from.value = 0;
+            from.visible = false;
+        };
+        const vector = grid.getColumn(columnIndex);
+        const testForDone = fromIndex => fromIndex >= vector.length;
+        let fromIndex = 0;
+        let toIndex = -1;
+        const didChangeThisPass = slide(fromIndex, toIndex, vector, advance, swap, merge, testForDone);
+        didIDoIt = didIDoIt || didChangeThisPass;
+    }
+    return didIDoIt;
+}
+
 const slideLeft = (grid) => {
     let didIDoIt = false;
+    const advance = i => i + 1;
     for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
-        lastIndex = -1;
-        for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex++;
-                if (lastIndex != columnIndex) {
-                    grid.swapTiles(rowIndex, columnIndex, rowIndex, lastIndex);
-                    didIDoIt = true;
-                }
-            }
-        }
+        const swap = (from, to) => {
+            grid.swapTiles(rowIndex, from, rowIndex, to);
+            const tempTile = vector[to];
+            vector[to] = vector[from];
+            vector[from] = tempTile;
+        };
+        const merge = (from, to) => {
+            to.value++;
+            from.value = 0;
+            from.visible = false;
+        };
+        const vector = grid.getRow(rowIndex);
+        const testForDone = fromIndex => fromIndex >= vector.length;
+        let fromIndex = 0;
+        let toIndex = -1;
+        const didChangeThisPass = slide(fromIndex, toIndex, vector, advance, swap, merge, testForDone);
+        didIDoIt = didIDoIt || didChangeThisPass;
+        
     }
     return didIDoIt;
 }
 
 const slideDown = (grid) => {
     let didIDoIt = false;
+    const advance = i => i - 1;
     for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
-        lastIndex = grid.numRows;
-        for (let rowIndex = grid.numRows - 1; rowIndex >= 0; rowIndex -= 1) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex--;
-                if (lastIndex != rowIndex) {
-                    grid.swapTiles(rowIndex, columnIndex, lastIndex, columnIndex);
-                    didIDoIt = true;
-                }
-            }
-        }
+        const swap = (from, to) => {
+            grid.swapTiles(from, columnIndex, to, columnIndex);
+            const tempTile = vector[to];
+            vector[to] = vector[from];
+            vector[from] = tempTile;
+        };
+        const merge = (from, to) => {
+            to.value++;
+            from.value = 0;
+            from.visible = false;
+        };
+        const vector = grid.getColumn(columnIndex);
+        const testForDone = fromIndex => fromIndex < 0;
+        let fromIndex = vector.length - 1;
+        let toIndex = vector.length;
+        const didChangeThisPass = slide(fromIndex, toIndex, vector, advance, swap, merge, testForDone);
+        didIDoIt = didIDoIt || didChangeThisPass;
     }
     return didIDoIt;
 }
 
 const slideRight = (grid) => {
     let didIDoIt = false;
+    const advance = i => i - 1;
     for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
-        lastIndex = grid.numColumns;
-        for (let columnIndex = grid.numColumns - 1; columnIndex >= 0; columnIndex -= 1) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex--;
-                if (lastIndex != columnIndex) {
-                    grid.swapTiles(rowIndex, columnIndex, rowIndex, lastIndex);
-                    didIDoIt = true;
-                }
-            }
-        }
+        const swap = (from, to) => {
+            grid.swapTiles(rowIndex, from, rowIndex, to);
+            const tempTile = vector[to];
+            vector[to] = vector[from];
+            vector[from] = tempTile;
+        };
+        const merge = (from, to) => {
+            to.value++;
+            from.value = 0;
+            from.visible = false;
+        };
+        const vector = grid.getRow(rowIndex);
+        const testForDone = fromIndex => fromIndex < 0;
+        let fromIndex = vector.length - 1;
+        let toIndex = vector.length;
+        const didChangeThisPass = slide(fromIndex, toIndex, vector, advance, swap, merge, testForDone);
+        didIDoIt = didIDoIt || didChangeThisPass;
     }
     return didIDoIt;
 }
 
 const canSlideUp = (grid) => {
-    canIDoIt = false;
-    for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
-        lastIndex = -1;
-        for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex++;
-                if (lastIndex != rowIndex) {
-                    canIDoIt = true;
-                }
-            }
-        }
-    }
-    return canIDoIt;
-}
-
-const canSlideLeft = (grid) => {
-    let canIDoIt = false;
-    for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
-        lastIndex = -1;
-        for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex++;
-                if (lastIndex != columnIndex) {
-                    canIDoIt = true;
-                }
-            }
-        }
-    }
-    return canIDoIt;
+    const cloneGrid = grid.clone();
+    return slideUp(cloneGrid);
 }
 
 const canSlideDown = (grid) => {
-    let canIDoIt = false;
-    for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
-        lastIndex = grid.numRows;
-        for (let rowIndex = grid.numRows - 1; rowIndex >= 0; rowIndex -= 1) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex--;
-                if (lastIndex != rowIndex) {
-                    canIDoIt = true;
-                }
-            }
-        }
-    }
-    return canIDoIt;
+    const cloneGrid = grid.clone();
+    return slideDown(cloneGrid);
+}
 
+const canSlideLeft = (grid) => {
+    const cloneGrid = grid.clone();
+    return slideLeft(cloneGrid);
 }
 
 const canSlideRight = (grid) => {
-    let canIDoIt = false;
-    for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
-        lastIndex = grid.numColumns;
-        for (let columnIndex = grid.numColumns - 1; columnIndex >= 0; columnIndex -= 1) {
-            const tile = grid.getTile(rowIndex, columnIndex);
-            if (tile.visible) {
-                lastIndex--;
-                if (lastIndex != columnIndex) {
-                    canIDoIt = true;
-                }
-            }
-        }
-    }
-    return canIDoIt;
+    const cloneGrid = grid.clone();
+    return slideRight(cloneGrid);
 }
 
 const gameIsLost = (grid) => {
+    // return !canSlideUp(grid);
+    // return false;
     return !canSlideUp(grid)
         && !canSlideRight(grid)
         && !canSlideDown(grid)
@@ -286,4 +393,40 @@ const checkForEnd = (grid) => {
     if (gameIsLost(grid)) {
         alert('A loser is you!');
     }
-}
\ No newline at end of file
+}
+
+const makeDevGrid = (matrix) => {
+    const numRows = matrix.length;
+    const numColumns = matrix[0].length;
+    const initialValue = makeTile(0, false, 0, 0);
+    const grid = makeGrid(numRows, numColumns, initialValue);
+    for (let rowIndex = 0; rowIndex < numRows; rowIndex++) {
+        const row = matrix[rowIndex];
+        for (let colIndex = 0; colIndex < numColumns; colIndex++) {
+            const value = row[colIndex];
+            const tile = grid.getTile(rowIndex, colIndex);
+            tile.value = value;
+            tile.visible = value > 0;
+        }
+    }
+    return grid;
+}
+/*
+[0,0,0,0],
+[0,0,1,0],
+[0,0,0,0],
+[2,1,2,2],
+can't slide down.
+[0,0,1,0],
+[0,0,0,0],
+[0,0,0,0],
+[3,2,3,0],
+can't slide down.
+can't slide left.
+up()
+[1,0,1,0],
+[0,0,3,0],
+[0,0,0,0],
+[3,2,0,0], either the 3 doesn't go up or the 1 bounces it back?
+// fixed
+*/