reserve X for BCI-algebra;
reserve x,y,z for Element of X;
reserve i,j,k,l,m,n for Nat;
reserve f,g for sequence of the carrier of X;
reserve B,P for non empty Subset of X;

theorem
  for X being quasi-commutative BCK-algebra holds (X is BCK-algebra of 0
  ,1,0,1 iff for x,y being Element of X holds x\y = (x\y)\y )
by BCIALG_3:28,Th49;
