Context : Enrico Letta was born in Pisa, Tuscany, to Giorgio Letta, an Abruzzo-born professor of mathematics who teaches probability theory at the University of Pisa (member of the Accademia dei Lincei and of the Accademia nazionale delle scienze), and Anna Banchi, a Sardinian born in Sassari and raised in Porto Torres of Tuscan origins. 
Subject : Enrico Letta 
Relation : occupation
What was Enrico Letta's career?