 For a fixed formula_6 the affine normal line to "M" at formula_7 may be parametrised by "t" where
The affine focal set is given geometrically as the infinitesimal intersections of the "n"-parameter family of affine normal lines.To calculate, choose an affine normal line, say at point "p"; then look at the affine normal lines at points infinitesimally close to "p" and see if any intersect the one at "p".If "p" is infinitesimally close to formula_9, then it may be expressed as formula_10 where formula_11 represents the infinitesimal difference.