reserve x,x0, r, s, h for Real,

  n for Element of NAT,
  rr, y for set,
  Z for open Subset of REAL,

  f, f1, f2 for PartFunc of REAL,REAL;

theorem Th12:
  rng arccot = ].0,PI.[
proof
  dom (cot|].0,PI.[) = ].0,PI.[ by Th2,RELAT_1:62;
  hence thesis by FUNCT_1:33;
end;
