diff --git a/schafkopf-logic/.gitignore b/schafkopf-logic/.gitignore
index f2f9e58..5bdfff6 100644
--- a/schafkopf-logic/.gitignore
+++ b/schafkopf-logic/.gitignore
@@ -1,2 +1,3 @@
 target
-Cargo.lock
\ No newline at end of file
+Cargo.lock
+shell.nix
\ No newline at end of file
diff --git a/schafkopf-logic/src/deck/card.rs b/schafkopf-logic/src/deck/card.rs
index 4f0a51c..a8ee4bd 100644
--- a/schafkopf-logic/src/deck/card.rs
+++ b/schafkopf-logic/src/deck/card.rs
@@ -10,6 +10,6 @@ pub struct Card {
 
 impl fmt::Display for Card {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{} {}", self.rank, self.suit)
+        write!(f, "{} {}", self.suit, self.rank)
     }
 }
\ No newline at end of file
diff --git a/schafkopf-logic/src/gamemode.rs b/schafkopf-logic/src/gamemode.rs
new file mode 100644
index 0000000..48c91ac
--- /dev/null
+++ b/schafkopf-logic/src/gamemode.rs
@@ -0,0 +1,135 @@
+use crate::deck::{Card, Suit, Rank};
+
+pub enum Gamemode {
+    Sauspiel(Suit),
+    Solo(Suit),
+    Wenz(Suit),
+    Geier(Suit),
+    Bettel,
+    Ramsch
+}
+
+impl Gamemode {
+    pub fn winning_card<'a>(&self, cards: [&'a Card; 4]) -> &'a Card  {
+        match self {
+            Gamemode::Sauspiel(_) | Gamemode::Ramsch | Gamemode::Bettel =>
+                winner_for_trump(Suit::Herz, cards),
+            Gamemode::Solo(solo_suit)   => winner_for_trump(*solo_suit, cards),
+            _ => cards[0],
+        }
+    }
+}
+
+fn winner_for_trump<'a>(trump_suit: Suit, cards: [&'a Card; 4]) -> &'a Card {
+    if cards.iter().any(|&c| is_trump(c, trump_suit)) {
+        // Highest trump wins
+        let winner_idx = cards
+            .iter()
+            .enumerate()
+            .filter(|&(_, &c)| is_trump(c, trump_suit))
+            .max_by_key(|&(_, &c)| trump_strength(c, trump_suit))
+            .map(|(i, _)| i)
+            .unwrap_or(0);
+        cards[winner_idx]
+    } else {
+        // No trump: highest of the led suit wins
+        let first_suit = cards[0].suit;
+        let winner_idx = cards
+            .iter()
+            .enumerate()
+            .filter(|&(_, &c)| c.suit == first_suit)
+            .max_by_key(|&(_, &c)| non_trump_strength(c.rank))
+            .map(|(i, _)| i)
+            .unwrap_or(0);
+        cards[winner_idx]
+    }
+}
+
+// A card is trump in Sauspiel if it's an Ober, an Unter, or of the trump suit.
+fn is_trump(card: &Card, trump_suit: Suit) -> bool {
+    card.rank == Rank::Ober || card.rank == Rank::Unter || card.suit == trump_suit
+}
+
+// Trump strength according to Schafkopf:
+// Obers: Eichel > Gras > Herz > Schell
+// Unters: Eichel > Gras > Herz > Schell
+// Then trump suit cards: A > 10 > K > 9 > 8 > 7
+fn trump_strength(card: &Card, trump_suit: Suit) -> u16 {
+    match card.rank {
+        Rank::Ober => 300 + ober_unter_suit_strength(card.suit),
+        Rank::Unter => 200 + ober_unter_suit_strength(card.suit),
+        _ if card.suit == trump_suit => 100 + non_trump_strength(card.rank) as u16,
+        _ => 0,
+    }
+}
+
+// Suit precedence for Obers/Unters: Eichel > Gras > Herz > Schell
+fn ober_unter_suit_strength(s: Suit) -> u16 {
+    match s {
+        Suit::Eichel => 4,
+        Suit::Gras   => 3,
+        Suit::Herz   => 2,
+        Suit::Schell => 1,
+    }
+}
+
+// Non-trump (following suit) strength: A > 10 > K > 9 > 8 > 7
+fn non_trump_strength(rank: Rank) -> u8 {
+    match rank {
+        Rank::Ass    => 6,
+        Rank::Zehn   => 5,
+        Rank::Koenig => 4,
+        Rank::Neun   => 3,
+        Rank::Acht   => 2,
+        Rank::Sieben => 1,
+        _ => 0, // Ober/Unter are trumps, handled elsewhere
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::deck::{Card, Suit, Rank};
+
+    fn card(suit: Suit, rank: Rank) -> Card {
+        Card { suit, rank }
+    }
+
+    #[test]
+    fn sauspiel_trump_beats_non_trump() {
+        // In Sauspiel, trumps are all Obers, all Unters, and Herz.
+        let c0 = card(Suit::Eichel, Rank::Ass);    // lead (non-trump)
+        let c1 = card(Suit::Gras,   Rank::Ober);   // trump (Ober)
+        let c2 = card(Suit::Herz,   Rank::Zehn);   // trump (Herz suit)
+        let c3 = card(Suit::Gras,   Rank::Ass);    // non-trump
+
+        let winner = Gamemode::Sauspiel(Suit::Eichel).winning_card([&c0, &c1, &c2, &c3]);
+        // Ober beats Herz trumps due to higher trump tier
+        assert_eq!(winner, &c1);
+    }
+
+    #[test]
+    fn sauspiel_follow_suit_highest_non_trump_when_no_trumps() {
+        // No Obers/Unters and no Herz => follow led suit, highest wins (A > 10 > K > 9 > 8 > 7)
+        let c0 = card(Suit::Eichel, Rank::Koenig); // lead
+        let c1 = card(Suit::Gras,   Rank::Ass);
+        let c2 = card(Suit::Eichel, Rank::Ass);    // same suit as lead, highest
+        let c3 = card(Suit::Schell, Rank::Zehn);
+
+        let winner = Gamemode::Sauspiel(Suit::Gras).winning_card([&c0, &c1, &c2, &c3]);
+        assert_eq!(winner, &c2);
+    }
+
+    #[test]
+    fn solo_uses_declared_suit_as_trump() {
+        // In Solo(Gras), trumps are all Obers, all Unters, and all Gras.
+        // Avoid Obers/Unters to focus on the solo suit behaving as trump.
+        let c0 = card(Suit::Herz,   Rank::Koenig); // lead
+        let c1 = card(Suit::Gras,   Rank::Zehn);   // trump (solo suit)
+        let c2 = card(Suit::Eichel, Rank::Ass);
+        let c3 = card(Suit::Schell, Rank::Ass);
+
+        let winner = Gamemode::Solo(Suit::Gras).winning_card([&c0, &c1, &c2, &c3]);
+        assert_eq!(winner, &c1);
+    }
+}
\ No newline at end of file
diff --git a/schafkopf-logic/src/main.rs b/schafkopf-logic/src/main.rs
index 30fa20b..ea1edcb 100644
--- a/schafkopf-logic/src/main.rs
+++ b/schafkopf-logic/src/main.rs
@@ -1,5 +1,8 @@
 mod deck;
-use deck::Deck;
+mod gamemode;
+
+use deck::{Deck, Suit, Card, Rank};
+use gamemode::Gamemode;
 
 fn main() {
     let mut deck = Deck::new();
@@ -26,4 +29,23 @@ fn main() {
     for card in hand4.iter() {
         println!("{}", card)
     }
+
+    let mode = Gamemode::Solo(Suit::Gras);
+
+    //let trick: [&Card; 4] = [&hand1[0], &hand2[0], &hand3[0], &hand4[0]];
+    let c1 = Card { suit: Suit::Schell, rank: Rank::Zehn };
+    let c2 = Card { suit: Suit::Schell, rank: Rank::Ass };
+    let c3 = Card { suit: Suit::Schell, rank: Rank::Unter };
+    let c4 = Card { suit: Suit::Gras, rank: Rank::Sieben };
+
+    let trick: [&Card; 4] = [&c1, &c2, &c3, &c4];
+
+
+    for card in trick.iter() {
+        println!("{}", card)
+    }
+    println!("\n");
+
+    let winner = mode.winning_card(trick);
+    println!("\nWinning card: {}", winner);
 }