... with√ = 0, bd > (and a = 1 ), has √ IPCB If H(b, 0, 0) = + 2, and if H( 0,0 ,d) = + 2, then (1. 2) with c = d = 0, b > and with c = b = 0, d > (and a = 1) has IPCB (b) If c > and H(b,c,d) = 1, then the ... 5.3 ( 1) If c > 0, then solutions (un ) of (5. 1) are rational if and only if the ’s are rational, when b, c, d are rational Then, in this case, a rational periodic solution of (5. 1) may have only ... respect to the diagonal, contains the points P = (−1/ , 0 ), P = ( 0, −1/ ), and the three distinct points Fi = (1/( fi − ), 1/( fi − )) , i = 1,2 , 3, except if b = d = 0, when F2 is the point at in nity...