The boundary of a convex set is always a convex curve. The intersection of all convex sets containing a given subset A of Euclidean space is called the convex hull of A. It is the smallest convex set containing A.
Rector (ecclesiastical) A rector is, in an ecclesiastical sense, a cleric who functions as an administrative leader in some Christian denominations, and in Islam. In contrast, a vicar is also a cleric but functions as an assistant and representative of an administrative leader.
Thus, the tithes of a parish are the legal property of the person who holds the office of rector, and are not the property of his vicar, who is not an office-holder but a mere employee, remunerated by a stipend, i.e. a salary, payable by his employer the rector.