reserve X for BCI-algebra;
reserve x,y,z,u,a,b for Element of X;
reserve IT for non empty Subset of X;

theorem
  X is alternative implies (x\(x\y))\(y\x) = x
proof
  assume
A1: X is alternative;
  then x\(x\y)=y by Th76;
  hence thesis by A1,Th76;
end;
