We consider the
linear equations
-

-

-

over
.
- Determine a
basis
of the solution space of this linear system.
- Extend the basis
to a basis
of the solution space of the linear system consisting of the first two equations.
- Extend the basis
to a basis
of the solution space of the linear system consisting of the first equation alone.
- Extend the basis
to a basis
of the total space
.