"The number 1 has this property, since the only positive integer not exceeding 1 is 1 itself, and therefore the sum is 1. This is a constructive proof."
"the set of students at your school who either are not sophomores or are not taking ds"
"有向图的邻接矩阵定义中,aij=1,若{vi,vj}是G的一条边"
"但是删除顶点v和所有与v关联的边.."
"证明:如果n是不能被2或3整除的整数,则n^2 - 1能被24整除"
"Many people fnd it confusing that "p only if q" expresses the same thing as "if p then q." To remember this, note that "p only if q" says that p cannot be true when q is not true. That is, the statement is false if p is true, but q is false. When p is false, q may be either true or false, because th"