It is the set of all convex combinations of the unit coordinate vectors. Sometimes it is convenient to number the indices of a vector in Rm+1 using 0,...,m instead of 1,...,m+1, in which case we may write ∆m = ˆ (α0,...,αm) ∈ R m+1: Xm i=0 αi = 1, αi ⩾ 0, i = 0,...,m ˙ 1.1.6 Exercise (Examples of convex sets) Prove the following.