reserve p,q,r,th,th1 for Real;
reserve n for Nat;

theorem Th36:
  tanh is_differentiable_on REAL & diff(tanh,p)=1/(cosh.p)^2
proof
  [#]REAL is open Subset of REAL & for p st p in REAL holds tanh
  is_differentiable_in p by Lm22,Lm23;
  hence thesis by Lm22,Lm23,Th30,FDIFF_1:9;
end;
