theorem
  (ex r st 0<r & f|].x0-r,x0.[ is increasing & f|].x0,x0+r.[ is
  decreasing & not f|].x0-r,x0.[ is bounded_above & not f|].x0,x0+r.[ is
bounded_above) & (for r1,r2 st r1<x0 & x0<r2 ex g1,g2 st r1<g1 & g1<x0 & g1 in
  dom f & g2<r2 & x0<g2 & g2 in dom f) implies f is_divergent_to+infty_in x0
by Th20;
