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--- Introduction ---
This is a computing exercise on the intersection of two affine subspaces
(lines, planes, or hyperplanes) in a plane or a space of higher dimension.
It can present the two starting subspaces under several forms, and
can ask you to describe the intersection under one of several forms.
The case where the intersection is a unique point is often quite easy.
Otherwise, computations of linear algebra will often be necessary to solve