Question: The Districts of Trentino-Alto Adige/Südtirol are a subdivision of the two Italian autonomous provinces of Trento and Bolzano, they were established by a decree of the President of Italy on which date, the President of the Italian Republic,  is the head of state of Italy and, in that role, represents national unity and guarantees that Italian politics comply with the Constitution?

Context paragraphs:
Italian presidential election, 1964: The Italian presidential election of 1964 was held in Italy on 16 – 28 December 1964, following the resignation of incumbent President Antonio Segni on 6 December 1964, because of a thrombosis.  Only members of Parliament and regional delegates are entitled to vote.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

Districts of Trentino-Alto Adige/Südtirol: The Districts of Trentino-Alto Adige/Südtirol are a subdivision of the two Italian autonomous provinces of Trento ("Trentino") and Bolzano ("South Tyrol").  They were established by a decree of the President of Italy (Nr.  987) on 10 June 1955.

Italian presidential election, 2015: The Italian presidential election of 2015 was held in Italy on 29–31 January 2015, following the resignation of incumbent President Giorgio Napolitano on 14 January 2015.  Only members of Parliament and regional delegates are entitled to vote.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

Italian presidential election, 1948: The Italian presidential election of 1948 was held in Italy on 10 – 11 May 1948, following the resignation of outgoing President Enrico De Nicola.  Only members of Parliament are entitled to vote and this election was the first one voted by a regular Parliament.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

Italian presidential election, 1962: The Italian presidential election of 1962 was held in Italy on 2 – 6 May 1962.  Only members of Parliament are entitled to vote.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

South Tyrol: South Tyrol (German and Ladin: "Südtirol" ] ; Italian: "Sudtirolo" ] ), also known by its alternative Italian name Alto Adige (] ), is an autonomous province in northern Italy.  It is one of the two autonomous provinces that make up the autonomous region of Trentino-Alto Adige/Südtirol.  The province has an area of 7400 km2 and a total population of 511,750 inhabitants (31.12.2011).  Its capital is the city of Bolzano (German: "Bozen"; Ladin: "Balsan" or "Bulsan").

Italian presidential election, 1955: The Italian presidential election of 1955 was held in Italy on 28 – 29 April 1955.  Only members of Parliament are entitled to vote.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

Italian presidential election, 1971: The Italian presidential election of 1971 was held in Italy on 9 – 24 December 1971.  Only members of Parliament and regional delegates are entitled to vote.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

President of Italy: The President of the Italian Republic (Italian: "Presidente della Repubblica Italiana" ) is the head of state of Italy and, in that role, represents national unity and guarantees that Italian politics comply with the Constitution.  The president's term of office lasts for seven years.  The 11th President of the Republic, Giorgio Napolitano, was elected on 10 May 2006, and elected to a second term for the first time in Italian Republic history, on 20 April 2013.  On 31 January 2015, the incumbent President, former Constitutional judge Sergio Mattarella, was elected at the fourth ballot with 665 votes out of 1,009.

Italian presidential election, 1978: The Italian presidential election of 1978 was held in Italy on 29 June – 8 July 1978, following the resignation of incumbent President Giovanni Leone on 15 June 1978, because of the Lockheed bribery scandals.  Only members of Parliament and regional delegates are entitled to vote.  As head of state of the Italian Republic, the President has a role of representation of national unity and guarantees that Italian politics comply with the Italian Constitution, in the framework of a parliamentary system.

Supporting paragraphs: Districts of Trentino-Alto Adige/Südtirol President of Italy
Answer: 10 June 1955