theorem
  (ex r st 0<r & f|].x0-r,x0.[ is increasing & not f|].x0-r,x0.[ is
  bounded_above) & (for r st r<x0 ex g st r<g & g<x0 & g in dom f) implies f
  is_left_divergent_to+infty_in x0 by Th25;
