Here we consider a so called (scalar) normal system of n ordinary linear differential equations which is a system of the form $$\left\{ {\begin{array}{*{20}{c}} {{{{x'}}_{1}} = {{a}_{{11}}}(t){{x}_{1}} + {{a}_{{12}}}(t){{x}_{2}} + ... + {{a}_{{1n}}}(t){{x}_{n}} + {{f}_{1}}(t),} \\ {{{{x'}}_{2}} = {{a}_{{21}}}(t){{x}_{1}} + {{a}_{{22}}}(t){{x}_{2}} + ... + {{a}_{{2n}}}(t){{x}_{n}} + {{f}_{2}}(t),} \\ {.\;\,.\;\,.\,\,.\;\,.\;\,..\;\,.\;\,.\,.\;\,.\;\,.\;.\;\,.\;\,..\;\,.\;\,..\;\,.\;\,..\;\,.\;\,..\;\,.\;\,.\,.\;\,.\;\,..\;\,.\;\,.\;\,.} \\ {{{{x'}}_{n}} = {{a}_{{n1}}}(t){{x}_{1}} + {{a}_{{n2}}}(t){{x}_{2}} + ... + {{a}_{{nn}}}(t){{x}_{n}} + {{f}_{n}}(t),} \\ \end{array} } \right.$$ (8.1) where a ij (t) and f i (t) are complex-valued functions defined on an interval ]a, b[ of the real axis (one or both of the points a and b can be infinitely large, i, j = 1, 2,..., n). System (8.1) is equivalent to a single matrix equation of the form $$X' = A\left( t \right)X + F\left( t \right)$$ (8.2)