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 Th40:
  arccot 1 = PI/4 & arccot.1 = PI/4
proof
A1: PI/4 < PI by Lm9,XXREAL_1:4;
  arccot 1 = PI/4 by A1,Th18,Th36;
  hence thesis;
end;
