If the abbrevation of AYFY is A=ALUM,.Y=INSIDE SHEATH,F=FLAT,Y=OUTSIDE SHEATH,HOW Y=SHEATH for aluminium cond.?

sir, i came to know that the abbrevation of AYFY conductor from yahoo answer.i,e A = ALUMINIUM,Y = INNER SHEATH,F = FLAT ARMOURED,Y = OUTER SHEATH, here my doubt is how it is possible to put Y for inner sheath and outer sheath. definetly some meaning should be there .what is the meaning of this Y. for A and F,taken their first letter (aluminium,flat armoured)