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
  arccot 0 = PI/2 & arccot.0 = PI/2
proof
A1: PI/2 < PI/1 by XREAL_1:76;
  arccot 0 = PI/2 by A1,Th36,Th42;
  hence thesis;
end;
