diff --git a/.idea/php-docker-settings.xml b/.idea/php-docker-settings.xml
new file mode 100644
index 0000000..14d87ab
--- /dev/null
+++ b/.idea/php-docker-settings.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="PhpDockerContainerSettings">
+    <list>
+      <map>
+        <entry key="ae79c5b5-b3e4-4c78-88a8-c2210ac05394">
+          <value>
+            <DockerContainerSettings>
+              <option name="version" value="1" />
+              <option name="volumeBindings">
+                <list>
+                  <DockerVolumeBindingImpl>
+                    <option name="containerPath" value="/opt/project" />
+                    <option name="hostPath" value="$PROJECT_DIR$" />
+                  </DockerVolumeBindingImpl>
+                </list>
+              </option>
+            </DockerContainerSettings>
+          </value>
+        </entry>
+      </map>
+    </list>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/php-test-framework.xml b/.idea/php-test-framework.xml
new file mode 100644
index 0000000..5ff2c25
--- /dev/null
+++ b/.idea/php-test-framework.xml
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="PhpTestFrameworkVersionCache">
+    <tools_cache>
+      <tool tool_name="PHPUnit">
+        <cache>
+          <versions>
+            <info id="interpreter-ae79c5b5-b3e4-4c78-88a8-c2210ac05394" version="8.1.6" />
+          </versions>
+        </cache>
+      </tool>
+    </tools_cache>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/php.xml b/.idea/php.xml
index f6159c8..ac353f2 100644
--- a/.idea/php.xml
+++ b/.idea/php.xml
@@ -1,4 +1,89 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="PhpInterpreters">
+    <interpreters>
+      <interpreter id="ae79c5b5-b3e4-4c78-88a8-c2210ac05394" name="laradock_php-fpm:latest" home="docker://DATA" debugger_id="php.debugger.XDebug">
+        <remote_data DOCKER_ACCOUNT_NAME="Docker" DOCKER_IMAGE_NAME="laradock_php-fpm:latest" DOCKER_REMOTE_PROJECT_PATH="/opt/project" INTERPRETER_PATH="php" HELPERS_PATH="/opt/.phpstorm_helpers" INITIALIZED="false" VALID="true" RUN_AS_ROOT_VIA_SUDO="false" />
+      </interpreter>
+    </interpreters>
+  </component>
+  <component name="PhpInterpretersPhpInfoCache">
+    <phpInfoCache>
+      <interpreter name="laradock_php-fpm:latest">
+        <phpinfo binary_type="PHP" php_cli="/usr/local/bin/php" path_separator=":" version="7.2.15">
+          <additional_php_ini>/usr/local/etc/php/conf.d/docker-php-ext-bcmath.ini, /usr/local/etc/php/conf.d/docker-php-ext-calendar.ini, /usr/local/etc/php/conf.d/docker-php-ext-exif.ini, /usr/local/etc/php/conf.d/docker-php-ext-gd.ini, /usr/local/etc/php/conf.d/docker-php-ext-imagick.ini, /usr/local/etc/php/conf.d/docker-php-ext-imap.ini, /usr/local/etc/php/conf.d/docker-php-ext-intl.ini, /usr/local/etc/php/conf.d/docker-php-ext-ldap.ini, /usr/local/etc/php/conf.d/docker-php-ext-mysqli.ini, /usr/local/etc/php/conf.d/docker-php-ext-opcache.ini, /usr/local/etc/php/conf.d/docker-php-ext-pcntl.ini, /usr/local/etc/php/conf.d/docker-php-ext-pdo_mysql.ini, /usr/local/etc/php/conf.d/docker-php-ext-pdo_pgsql.ini, /usr/local/etc/php/conf.d/docker-php-ext-pgsql.ini, /usr/local/etc/php/conf.d/docker-php-ext-rdkafka.ini, /usr/local/etc/php/conf.d/docker-php-ext-redis.ini, /usr/local/etc/php/conf.d/docker-php-ext-soap.ini, /usr/local/etc/php/conf.d/docker-php-ext-sodium.ini, /usr/local/etc/php/conf.d/docker-php-ext-xdebug.ini, /usr/local/etc/php/conf.d/docker-php-ext-zip.ini, /usr/local/etc/php/conf.d/laravel.ini, /usr/local/etc/php/conf.d/opcache.ini, /usr/local/etc/php/conf.d/xdebug.ini</additional_php_ini>
+          <configuration_file />
+          <configuration_options>
+            <configuration_option name="include_path" value=".:/usr/local/lib/php" />
+          </configuration_options>
+          <debuggers>
+            <debugger_info debugger="xdebug" debugger_version="2.7.2">
+              <debug_extensions />
+            </debugger_info>
+          </debuggers>
+          <loaded_extensions>
+            <extension name="Core" />
+            <extension name="PDO" />
+            <extension name="Phar" />
+            <extension name="Reflection" />
+            <extension name="SPL" />
+            <extension name="SimpleXML" />
+            <extension name="Zend OPcache" />
+            <extension name="bcmath" />
+            <extension name="calendar" />
+            <extension name="ctype" />
+            <extension name="curl" />
+            <extension name="date" />
+            <extension name="dom" />
+            <extension name="exif" />
+            <extension name="fileinfo" />
+            <extension name="filter" />
+            <extension name="ftp" />
+            <extension name="gd" />
+            <extension name="hash" />
+            <extension name="iconv" />
+            <extension name="imagick" />
+            <extension name="imap" />
+            <extension name="intl" />
+            <extension name="json" />
+            <extension name="ldap" />
+            <extension name="libxml" />
+            <extension name="mbstring" />
+            <extension name="mysqli" />
+            <extension name="mysqlnd" />
+            <extension name="openssl" />
+            <extension name="pcntl" />
+            <extension name="pcre" />
+            <extension name="pdo_mysql" />
+            <extension name="pdo_pgsql" />
+            <extension name="pdo_sqlite" />
+            <extension name="pgsql" />
+            <extension name="posix" />
+            <extension name="rdkafka" />
+            <extension name="readline" />
+            <extension name="redis" />
+            <extension name="session" />
+            <extension name="soap" />
+            <extension name="sodium" />
+            <extension name="sqlite3" />
+            <extension name="standard" />
+            <extension name="tokenizer" />
+            <extension name="xdebug" />
+            <extension name="xml" />
+            <extension name="xmlreader" />
+            <extension name="xmlwriter" />
+            <extension name="zip" />
+            <extension name="zlib" />
+          </loaded_extensions>
+        </phpinfo>
+      </interpreter>
+    </phpInfoCache>
+  </component>
   <component name="PhpProjectSharedConfiguration" php_language_level="7.3" />
+  <component name="PhpUnit">
+    <phpunit_settings>
+      <PhpUnitSettings load_method="PHPUNIT_PHAR" configuration_file_path="$PROJECT_DIR$/phpunit.xml" custom_loader_path="" phpunit_phar_path="$PROJECT_DIR$/tools/phpunit.phar" use_configuration_file="true" />
+      <phpunit_by_interpreter interpreter_id="ae79c5b5-b3e4-4c78-88a8-c2210ac05394" load_method="PHPUNIT_PHAR" configuration_file_path="/opt/project/phpunit.xml" custom_loader_path="" phpunit_phar_path="/opt/project/tools/phpunit.phar" use_configuration_file="true" />
+    </phpunit_settings>
+  </component>
 </project>
\ No newline at end of file
diff --git a/src/Bread.php b/src/Bread.php
new file mode 100644
index 0000000..c76c5a6
--- /dev/null
+++ b/src/Bread.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+namespace ClansOfCaledonia;
+
+final class Bread extends Good
+{
+    public function isBread(): bool
+    {
+        return true;
+    }
+}
diff --git a/src/Cheese.php b/src/Cheese.php
new file mode 100644
index 0000000..da08ad4
--- /dev/null
+++ b/src/Cheese.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+namespace ClansOfCaledonia;
+
+final class Cheese extends Good
+{
+    public function isCheese(): bool
+    {
+        return true;
+    }
+}
diff --git a/src/Good.php b/src/Good.php
index 2e540c6..45f0f9e 100644
--- a/src/Good.php
+++ b/src/Good.php
@@ -8,8 +8,53 @@ public static function milk(): self
         return new Milk;
     }
 
+    public static function bread(): self
+    {
+        return new Bread;
+    }
+
+    public static function whisky(): self
+    {
+        return new Whisky;
+    }
+
+    public static function cheese(): self
+    {
+        return new Cheese;
+    }
+
+    public static function wool(): self
+    {
+        return new Wool;
+    }
+
+    public static function grain(): self
+    {
+        return new Grain;
+    }
+
+    public function isWhisky(): bool
+    {
+        return false;
+    }
+
+    public function isBread(): bool
+    {
+        return false;
+    }
+
+    public function isWool(): bool
+    {
+        return false;
+    }
+
     public function isMilk(): bool
     {
         return false;
     }
+
+    public function isCheese(): bool
+    {
+        return false;
+    }
 }
diff --git a/src/Grain.php b/src/Grain.php
new file mode 100644
index 0000000..645ea87
--- /dev/null
+++ b/src/Grain.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+namespace ClansOfCaledonia;
+
+final class Grain extends Good
+{
+    public function isGrain(): bool
+    {
+        return true;
+    }
+}
diff --git a/src/Market.php b/src/Market.php
index cfe5ae3..71625a4 100644
--- a/src/Market.php
+++ b/src/Market.php
@@ -3,15 +3,38 @@
 
 final class Market
 {
-    public function priceFor(Good $milk): Pound
+    /**
+     * @var PriceList
+     */
+    private $milkPrices;
+    /**
+     * @var PriceList
+     */
+    private $whiskyPrices;
+
+    public function __construct(PriceList $milkPrices, PriceList $whiskyPrices)
     {
-        return new Pound(5);
+        $this->milkPrices = $milkPrices;
+        $this->whiskyPrices = $whiskyPrices;
+    }
+
+    public function priceFor(Good $good): Pound
+    {
+        if($good->isMilk()){
+            return $this->milkPrices->current();
+        }
+
+        if($good->isWhisky()){
+            return $this->whiskyPrices->current();
+        }
     }
 
     public function sellTo(Offer $offer): Pound
     {
-        return new Pound(
-            $offer->amount()->amount() *
+        return (new Pound(
+            $offer->amount()->amount()
+        ))
+        ->multiply(
             $this->priceFor($offer->good())->amount()
         );
     }
diff --git a/src/Pound.php b/src/Pound.php
index 1be124e..9eb12d9 100644
--- a/src/Pound.php
+++ b/src/Pound.php
@@ -17,4 +17,9 @@ public function amount(): int
     {
         return $this->amount;
     }
+
+    public function multiply(int $multiplier)
+    {
+        return new self($this->amount * $multiplier);
+    }
 }
diff --git a/src/PriceList.php b/src/PriceList.php
index 8a6a231..cdb03c8 100644
--- a/src/PriceList.php
+++ b/src/PriceList.php
@@ -30,4 +30,16 @@ public function current(): Pound
     {
         return $this->prices[$this->position];
     }
+
+    public function decrement(int $steps = 1)
+    {
+        $this->position -= $steps;
+        return $this->position;
+    }
+
+    public function increment(int $steps = 1)
+    {
+        $this->position += $steps;
+        return $this->position;
+    }
 }
diff --git a/src/PriceListBuilder.php b/src/PriceListBuilder.php
index bc0da06..90dc407 100644
--- a/src/PriceListBuilder.php
+++ b/src/PriceListBuilder.php
@@ -3,6 +3,38 @@
 
 final class PriceListBuilder
 {
+    public function woolPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(3),
+            new Pound(3),
+            new Pound(4),
+            new Pound(4),
+            new Pound(5),
+            new Pound(5),
+            new Pound(6),
+            new Pound(6),
+            new Pound(7),
+            new Pound(8)
+        );
+    }
+
+    public function grainPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(3),
+            new Pound(3),
+            new Pound(4),
+            new Pound(5),
+            new Pound(6),
+            new Pound(6),
+            new Pound(7),
+            new Pound(7),
+            new Pound(8),
+            new Pound(8)
+        );
+    }
+
     public function milkPrices(): PriceList
     {
         return PriceList::fromList(
@@ -18,4 +50,53 @@ public function milkPrices(): PriceList
             new Pound(8)
         );
     }
+
+    public function breadPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(7),
+            new Pound(8),
+            new Pound(9),
+            new Pound(10),
+            new Pound(11),
+            new Pound(11),
+            new Pound(12),
+            new Pound(13),
+            new Pound(14),
+            new Pound(15)
+        );
+    }
+
+    public function cheesePrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(7),
+            new Pound(8),
+            new Pound(9),
+            new Pound(10),
+            new Pound(11),
+            new Pound(12),
+            new Pound(13),
+            new Pound(14),
+            new Pound(14),
+            new Pound(15)
+        );
+    }
+
+    public function whiskyPrices(): PriceList
+    {
+        return PriceList::fromList(
+            new Pound(8),
+            new Pound(9),
+            new Pound(10),
+            new Pound(11),
+            new Pound(12),
+            new Pound(13),
+            new Pound(13),
+            new Pound(14),
+            new Pound(15),
+            new Pound(16)
+        );
+    }
+
 }
diff --git a/src/Whisky.php b/src/Whisky.php
new file mode 100644
index 0000000..fcf4afb
--- /dev/null
+++ b/src/Whisky.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+namespace ClansOfCaledonia;
+
+final class Whisky extends Good
+{
+    public function isWhisky(): bool
+    {
+        return true;
+    }
+}
diff --git a/src/Wool.php b/src/Wool.php
new file mode 100644
index 0000000..e4ce4b9
--- /dev/null
+++ b/src/Wool.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+namespace ClansOfCaledonia;
+
+final class Wool extends Good
+{
+    public function isWool(): bool
+    {
+        return true;
+    }
+}
diff --git a/src/autoload.php b/src/autoload.php
index 1078cb5..0ab0230 100644
--- a/src/autoload.php
+++ b/src/autoload.php
@@ -7,8 +7,11 @@ function($class) {
         static $classes = null;
         if ($classes === null) {
             $classes = array(
+                'clansofcaledonia\\bread' => '/Bread.php',
+                'clansofcaledonia\\cheese' => '/Cheese.php',
                 'clansofcaledonia\\exception' => '/Exception.php',
                 'clansofcaledonia\\good' => '/Good.php',
+                'clansofcaledonia\\grain' => '/Grain.php',
                 'clansofcaledonia\\market' => '/Market.php',
                 'clansofcaledonia\\milk' => '/Milk.php',
                 'clansofcaledonia\\offer' => '/Offer.php',
@@ -16,7 +19,9 @@ function($class) {
                 'clansofcaledonia\\pound' => '/Pound.php',
                 'clansofcaledonia\\pricelist' => '/PriceList.php',
                 'clansofcaledonia\\pricelistbuilder' => '/PriceListBuilder.php',
-                'clansofcaledonia\\unit' => '/Unit.php'
+                'clansofcaledonia\\unit' => '/Unit.php',
+                'clansofcaledonia\\whisky' => '/Whisky.php',
+                'clansofcaledonia\\wool' => '/Wool.php'
             );
         }
         $cn = strtolower($class);
diff --git a/tests/MarketTest.php b/tests/MarketTest.php
index d01128e..7634ff5 100644
--- a/tests/MarketTest.php
+++ b/tests/MarketTest.php
@@ -15,14 +15,14 @@ final class MarketTest extends TestCase
 {
     public function testMilkCosts5PoundsInitially(): void
     {
-        $market = new Market;
+        $market = $this->createMarket();
 
         $this->assertEquals(new Pound(5), $market->priceFor(Good::milk()));
     }
 
     public function testMilkCanBeSoldToTheMarket(): Market
     {
-        $market = new Market;
+        $market = $this->createMarket();
 
         $payment = $market->sellTo(
             new Offer(
@@ -36,6 +36,21 @@ public function testMilkCanBeSoldToTheMarket(): Market
         return $market;
     }
 
+    public function testMilkCanBeBoughtFromTheMarket()
+    {
+        $market = $this->createMarket();
+
+        $payment = $market->buyFrom(
+            new Offer(
+                new Unit(3),
+                Good::milk()
+            )
+        );
+
+        $this->assertEquals(new Pound(10), $payment);
+
+    }
+
     /**
      * @depends testMilkCanBeSoldToTheMarket
      */
@@ -43,4 +58,29 @@ public function testSellingMilkToTheMarketReducesMilkPrice(Market $market): void
     {
         $this->assertEquals(new Pound(4), $market->priceFor(Good::milk()));
     }
+
+    public function testWhiskyCanBeSoldToTheMarket(): Market
+    {
+        $market = $this->createMarket();
+
+        $payment = $market->sellTo(
+            new Offer(
+                new Unit(3),
+                Good::whisky()
+            )
+        );
+
+        $this->assertEquals(new Pound(33), $payment);
+
+        return $market;
+    }
+
+    /**
+     * @return Market
+     */
+    protected function createMarket(): Market
+    {
+        $builder = new PriceListBuilder();
+        return new Market($builder->milkPrices(), $builder->whiskyPrices());
+    }
 }
diff --git a/tests/PoundTest.php b/tests/PoundTest.php
index 3d3ec6d..3213e2e 100644
--- a/tests/PoundTest.php
+++ b/tests/PoundTest.php
@@ -16,4 +16,14 @@ public function testHasAmount(): void
 
         $this->assertSame($amount, $p->amount());
     }
+
+    public function testItCanMultiplyByAnotherPound()
+    {
+        $firstPound = new Pound(5);
+
+        $resultingPound = $firstPound->multiply(6);
+
+        $this->assertInstanceOf(Pound::class, $resultingPound);
+        $this->assertEquals(30, $resultingPound->amount());
+    }
 }
diff --git a/tests/PriceListTest.php b/tests/PriceListTest.php
index aba7abb..a32496d 100644
--- a/tests/PriceListTest.php
+++ b/tests/PriceListTest.php
@@ -12,7 +12,57 @@ final class PriceListTest extends TestCase
 {
     public function testHasInitialPrice(): void
     {
-        $prices = PriceList::fromList(
+        $priceList = $this->getTestPriceList();
+
+        $this->assertEquals(new Pound(4), $priceList->current());
+    }
+
+    public function testCanDecrementPosition()
+    {
+        $priceList = $this->getTestPriceList();
+
+        $this->assertEquals(new Pound(4), $priceList->current());
+        $priceList->decrement();
+        $this->assertEquals(new Pound(3), $priceList->current());
+    }
+
+
+    public function testCanDecremenPositiontByMultipleSteps()
+    {
+        $priceList = $this->getTestPriceList();
+
+        $this->assertEquals(new Pound(4), $priceList->current());
+        $priceList->decrement(3);
+        $this->assertEquals(new Pound(1), $priceList->current());
+    }
+
+
+
+    public function testCanIncrementPosition()
+    {
+        $priceList = $this->getTestPriceList();
+
+        $this->assertEquals(new Pound(4), $priceList->current());
+        $priceList->increment();
+        $this->assertEquals(new Pound(5), $priceList->current());
+    }
+
+
+    public function testCanIncrementPositiontByMultipleSteps()
+    {
+        $priceList = $this->getTestPriceList();
+
+        $this->assertEquals(new Pound(4), $priceList->current());
+        $priceList->increment(3);
+        $this->assertEquals(new Pound(7), $priceList->current());
+    }
+
+    /**
+     * @return PriceList
+     */
+    protected function getTestPriceList(): PriceList
+    {
+        return PriceList::fromList(
             new Pound(1),
             new Pound(2),
             new Pound(3),
@@ -24,7 +74,5 @@ public function testHasInitialPrice(): void
             new Pound(9),
             new Pound(10)
         );
-
-        $this->assertEquals(new Pound(4), $prices->current());
     }
 }