Replacement means that an item is replaced or replaced by other items. Yes, there is substitution; No, there is no substitute.

In set theory, the permutation of a set is a bijection from the set to itself. In combinatorial mathematics, the traditional meaning of the word permutation is an ordered sequence, in which elements are not repeated, but there may be gaps. For example, 1, 2,4,3 can be called the arrangement of 1, 2,3,4,5,6, but it is not.