out ee;
off nat;
%off exp;
%-------- tangent field ----------------------

eex:=1;
eeu:=(2 - a**2*x**2)/(a*x*sqrt(4-a**2*x**2));
dee:=sqrt(eex**2 + eeu**2);

%-------- tangent unit field ----------------------
ttx:=eex/dee;
ttu:=eeu/dee;

%------------------------------

xs:=2/(a*cosh(a*s + d));
df(xs,s);

shut ee;
bye;
end;