Question: Who introduced a system of musical notation in the 14th century used in the area where the Ottoman slave trade flourished?

Knowledge 1: Black people
Due to the Ottoman slave trade that had flourished in the Balkans, the coastal town of Ulcinj in Montenegro had its own black community. As a consequence of the slave trade and privateer activity, it is told how until 1878 in Ulcinj 100 black people lived. The Ottoman Army also deployed an estimated 30,000 Black African troops and cavalrymen to its expedition in Hungary during the Austro-Turkish War of 1716–18. [SEP] Knowledge 2: Late Middle Ages
The main representatives of the new style, often referred to as ars nova as opposed to the ars antiqua, were the composers Philippe de Vitry and Guillaume de Machaut. In Italy, where the Provençal troubadours had also found refuge, the corresponding period goes under the name of trecento, and the leading composers were Giovanni da Cascia, Jacopo da Bologna and Francesco Landini. Prominent reformer of Orthodox Church music from the first half of 14th century was John Kukuzelis; he also introduced a system of notation widely used in the Balkans in the following centuries.
Knowledge 1: Sahara
In the 16th century the northern fringe of the Sahara, such as coastal regencies in present-day Algeria and Tunisia, as well as some parts of present-day Libya, together with the semi-autonomous kingdom of Egypt, were occupied by the Ottoman Empire. From 1517 Egypt was a valued part of the Ottoman Empire, ownership of which provided the Ottomans with control over the Nile Valley, the east Mediterranean and North Africa. The benefit of the Ottoman Empire was the freedom of movement for citizens and goods. Trade exploited the Ottoman land routes to handle the spices, gold and silk from the East, manufactures from Europe, and the slave and gold traffic from Africa. Arabic continued as the local language and Islamic culture was much reinforced. The Sahel and southern Sahara regions were home to several independent states or to roaming Tuareg clans. [SEP] Knowledge 2: Black people
Numerous communities of dark-skinned peoples are present in North Africa, some dating from prehistoric communities. Others are descendants of the historical Trans-Saharan trade in peoples and/or, and after the Arab invasions of North Africa in the 7th century, descendants of slaves from the Arab Slave Trade in North Africa.
Knowledge 1: Black people
Due to the Ottoman slave trade that had flourished in the Balkans, the coastal town of Ulcinj in Montenegro had its own black community. As a consequence of the slave trade and privateer activity, it is told how until 1878 in Ulcinj 100 black people lived. The Ottoman Army also deployed an estimated 30,000 Black African troops and cavalrymen to its expedition in Hungary during the Austro-Turkish War of 1716–18. [SEP] Knowledge 2: Classical music
It is in this time that the notation of music on a staff and other elements of musical notation began to take shape. This invention made possible the separation of the composition of a piece of music from its transmission; without written music, transmission was oral, and subject to change every time it was transmitted. With a musical score, a work of music could be performed without the composer's presence. The invention of the movable-type printing press in the 15th century had far-reaching consequences on the preservation and transmission of music.

Answer: John Kukuzelis