diff --git a/l6/lottery/config.yml b/l6/lottery/config.yml
deleted file mode 100644
index f7834a0..0000000
--- a/l6/lottery/config.yml
+++ /dev/null
@@ -1,5 +0,0 @@
-name: "Lottery"
-supportedstandards: []
-events:
-permissions:
-  - methods: []
diff --git a/l6/lottery/lottery_contract.go b/l6/lottery/lottery_contract.go
deleted file mode 100644
index d975d20..0000000
--- a/l6/lottery/lottery_contract.go
+++ /dev/null
@@ -1,13 +0,0 @@
-package lottery
-
-import (
-	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
-)
-
-func IsWinner(playerName string) bool {
-	if playerName == "demo" {
-		return true
-	}
-	random := runtime.GetRandom()
-	return random < 100
-}
diff --git a/l6/player/player_contract.go b/l6/player/player_contract.go
index 0f36e34..d3f90b2 100644
--- a/l6/player/player_contract.go
+++ b/l6/player/player_contract.go
@@ -5,6 +5,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/native/gas"
 	"github.com/nspcc-dev/neo-go/pkg/interop/native/std"
+	"github.com/nspcc-dev/neo-go/pkg/interop/neogointernal"
 	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
 	"github.com/nspcc-dev/neo-go/pkg/interop/storage"
 	"github.com/nspcc-dev/neo-go/pkg/interop/util"
@@ -56,19 +57,20 @@ func Items(playerName string) []string {
 }
 
 func BuyItem(playerName string, itemName string) {
-	itemPrice := itemPrices[itemName]
-
 	ctx := storage.GetContext()
 	player := getPlayer(ctx, playerName)
 	if !runtime.CheckWitness(player.owner) {
-		panic("not authorized")
+		panic("player not witnessed")
 	}
+
+	itemPrice := itemPrices[itemName]
 	if player.balance < itemPrice {
 		panic("insufficient balance")
 	}
 
-	player.balance -= itemPrice
 	addItemToInventory(player, itemName)
+	player.balance -= itemPrice
+
 	savePlayer(ctx, playerName, player)
 }
 
@@ -76,15 +78,12 @@ func SellItem(playerName string, itemName string) {
 	ctx := storage.GetContext()
 	player := getPlayer(ctx, playerName)
 	if !runtime.CheckWitness(player.owner) {
-		panic("not authorized")
+		panic("player not witnessed")
 	}
 
-	if !hasItemInInventory(player, itemName) {
-		panic("player has no specified item")
-	}
-
-	player.balance += itemPrices[itemName]
 	removeItemFromInventory(player, itemName)
+	player.balance += itemPrices[itemName]
+
 	savePlayer(ctx, playerName, player)
 }
 
@@ -92,7 +91,7 @@ func BuyItemForGas(playerName string, lotID int, itemPrice int, merchantHash int
 	ctx := storage.GetContext()
 	player := getPlayer(ctx, playerName)
 	if !runtime.CheckWitness(player.owner) {
-		panic("not authorized")
+		panic("player not witnessed")
 	}
 
 	itemName := contract.Call(merchantHash, "getItemName", contract.ReadOnly, lotID).(string)
@@ -111,12 +110,9 @@ func SellItemForGas(playerName string, itemName string, itemPrice int, merchantH
 	ctx := storage.GetContext()
 	player := getPlayer(ctx, playerName)
 	if !runtime.CheckWitness(player.owner) {
-		panic("not authorized")
+		panic("player not witnessed")
 	}
 
-	if !hasItemInInventory(player, itemName) {
-		panic("player has no specified item")
-	}
 	removeItemFromInventory(player, itemName)
 
 	balanceBefore := gas.BalanceOf(runtime.GetScriptContainer().Sender)
@@ -146,14 +142,13 @@ func savePlayer(ctx storage.Context, playerName string, player Player) {
 }
 
 func hasItemInInventory(player Player, itemName string) bool {
-	// Ugly loop, because the following standard syntax does not work:
-	// _, exists := player.itemCount[itemName]
-	for ownedName, count := range player.itemCount {
-		if ownedName == itemName {
-			return count > 0
-		}
+	// Standard syntax for go map does not work: _, exists := player.itemCount[itemName]
+	// So, we use HASKEY command to do this:
+	hasKey := neogointernal.Opcode2("HASKEY", player.itemCount, itemName).(bool)
+	if !hasKey {
+		return false
 	}
-	return false
+	return player.itemCount[itemName] > 0
 }
 
 func addItemToInventory(player Player, itemName string) {
@@ -164,6 +159,9 @@ func addItemToInventory(player Player, itemName string) {
 }
 
 func removeItemFromInventory(player Player, itemName string) {
+	if !hasItemInInventory(player, itemName) {
+		panic("player has no specified item")
+	}
 	player.itemCount[itemName] -= 1
 	if player.itemCount[itemName] == 0 {
 		delete(player.itemCount, itemName)