reserve x,x0, r,r1,r2 for Real,
      th for Real,

  rr for set,

  rseq for Real_Sequence;

theorem
  (-sqrt 2 <= r & r <= -1 & arcsec2 r = 3/4*PI implies r = -sqrt 2) & (-
  sqrt 2 <= r & r <= -1 & arcsec2 r = PI implies r = -1) by Th31,Th90;
