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.
Therefore, because a priest is designated head of a cathedral parish, he cannot be both rector and pastor, as a rector cannot canonically hold title over a parish (c.556). As a further example, the pastor of a parish is pastor (not rector) over both his parish and the parish church.