... R-modules in general is important and complex. However the study ofF -modules is short and simple – every vector space is free and every subspace is asummand. The core of classical linear algebra ... a and b are integers, not both zero, and G is the collection of all linear combinations of a and b, then G is a subgroup of Z, and itspositive generator is the greatest common divisor of a and ... r<n. Since r ∈ G, it must be 0, and g ∈ nZ.Now suppose a, b ∈ Z and at least one of a and b is non-zero.Theorem Let G be the set of all linear combinations of a and b, i.e., G ={ma + nb : m,...