A1: ( a > 1 & a + b > a + 0 ) by TA1, XREAL_1:6;
then log (a,(a + b)) > log (a,a) by POWER:57;
then log (a,(a + b)) > 1 by A1, POWER:52;
hence log (a,(a + b)) is heavy by TA1; :: thesis: verum