  We generalize the notions of singularities and ordinary points from linear
ordinary differential equations to D-finite systems. Ordinary points of a
D-finite system are characterized in terms of its formal power series
solutions. We also show that apparent singularities can be removed like in the
univariate case by adding suitable additional solutions to the system at hand.
Several algorithms are presented for removing and detecting apparent
singularities. In addition, an algorithm is given for computing formal power
series solutions of a D-finite system at apparent singularities.
