diff --git a/README.md b/README.md
index a368b22..3e7ba08 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ The current control scheme adheres to vim-like keybindings and is modal.
 
 ### Todo
 
-  - [ ] Game logic
+  - [x] Game logic
     - [x] Validate Sudokus
     - [x] Generate Sudokus
       - [x] Difficulties to choose
@@ -69,7 +69,7 @@ The current control scheme adheres to vim-like keybindings and is modal.
         - [x] Preselect numbers
         - [x] Edit Mode to (re)place numbers
         - [x] Markup Mode to mark where numbers could go
-          - [ ] Autoremove marks after placing number in edit mode
+          - [x] Autoremove marks after placing number in edit mode
         - [x] Go Mode to move to blocks 1-9
         - [x] Toggle Number/Mark with Space
         - [ ] Undo/Redo stack
diff --git a/src/main.rs b/src/main.rs
index 7059835..a4949b4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -16,7 +16,7 @@ use std::{io, time::Duration};
 
 fn main() {
     let mut screen = Screen::init(io::stdout());
-    let mut state = State::init(Difficulty::Expert);
+    let mut state = State::init(Difficulty::Mid);
     screen.draw_board().or_crash();
 
     loop {
diff --git a/src/state.rs b/src/state.rs
index ad71ad8..b2148a4 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -102,10 +102,11 @@ impl State {
 
     pub fn toggle_current_cell(&mut self) {
         if self.current_cell_is_modifiable() {
-            *self.current_cell() = if *self.current_cell() == self.preselection {
-                0
+            if *self.current_cell() == self.preselection {
+                *self.current_cell() = 0;
             } else {
-                self.preselection
+                *self.current_cell() = self.preselection;
+                self.delete_colliding_marks(self.preselection, self.cur_row, self.cur_col);
             }
         }
     }
@@ -116,6 +117,14 @@ impl State {
         }
     }
 
+    pub fn delete_colliding_marks(&mut self, num: u8, row: usize, col: usize) {
+        for i in 0..9 {
+            self.markups[i][col][num as usize - 1] = false;
+            self.markups[row][i][num as usize - 1] = false;
+            self.markups[row / 3 * 3 + i / 3][col / 3 * 3 + i % 3][num as usize - 1] = false;
+        }
+    }
+
     pub fn enter_mode(&mut self, mode: Mode) {
         match mode {
             Mode::Go => {