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.
In either tradition, a vicar can be the priest of a  chapel of ease , a building within the parish which is not the parish church. Non-resident canons led also to the institution of vicars choral, each canon having his own vicar, who sat in his stall in his absence (see Cathedral).