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 Th38:
  arccot (-1) = 3/4*PI & arccot.(-1) = 3/4*PI
proof
A1: 3/4*PI < PI by Lm10,XXREAL_1:4;
  arccot (-1) = 3/4*PI by A1,Th18,Th36;
  hence thesis;
end;
