Fixed a typo.

Envelope_2/doc_tex/Envelope_2/envelope.tex

@@ -97,7 +97,7 @@ compute the lower envelope of a set of lines. We read a set of
 points $\calP = p_1, \ldots, p_n$ from an input file, and compute the
 corresponding dual lines $\calP^{*} = p^{*}_1, \ldots, p^{*}_n$, where
 the line $p^{*}$ dual to a point $p = (p_x, p_y)$ is given by
-$y = p_x*x - p_y$. We then compute the convex hull of the point-set
+$y = p_x x - p_y$. We then compute the convex hull of the point-set
 $\calP$, using the fact that the lines that form the
 lower envelope of $\calP^{*}$ are dual to the points along the
 {\em upper} part of $\calP$'s convex hull, and the lines that form the