List specification (cont.)
npublic void remove(int i)
n Remove the element at the specified position.
n require:
n   0<=i && i<this.size()
n ensure:
n   this.size()==old.size-1
n   for i <= j < this.size()
n      this.get(j) == old.get(j+1)
npublic void set (int i, Student s)
n Replace the element at the specified position with the specified Student.
n require:
n   0 <= i && i < this.size()
n   s != null
n ensure:
n   this.get(i) == s