reserve
   a,b,c,x,y,z,A,B,C,X,Y for set,
   f,g for Function,
   V for SetValuation,
   P for Permutation of V,
   p,q,r,s for Element of HP-WFF,
   n for Element of NAT;

theorem Lm17: {} tohilb = (0,1) --> (1,0)
proof
reconsider X=Funcs({},{}) as non empty set;
reconsider I=id 1 as 1-defined Function;
set f=[:1,X:]*[:X,{1}:],
g=[:{1},X:]*[:X,{0}:],
ff=1-->1,
gg={1}-->0;
B0: ff=f & gg=g by FOMODEL0:73;
I +* ff +* gg = sw by CARD_1:49;
hence thesis by B0;
end;
