reserve a,b,c,d,x,y,w,z,x1,x2,x3,x4 , X for set;
reserve A for non empty set;
reserve i,j,k for Element of NAT;
reserve a,b,c,d for Real;
reserve y,r,s,x,t,w for Element of RAT+;
reserve z,z1,z2,z3,z4 for Quaternion;

theorem Th24:
  Rea <j> = 0 & Im1 <j> = 0 & Im2 <j> = 1 & Im3 <j> = 0 &
  Rea <k> = 0 & Im1 <k> = 0 & Im2 <k> = 0 & Im3 <k> = 1
 by Th16;
