The source code documentation for exponent-of says ;; Basically computes log of m base b. Except if m is not a power of b, we return nil. But (%i2) exp_of(k,m) := ?exponent\-of(k,m)$ (%i3) exp_of(6,2); (%o3) 1 (%i4) exp_of(2,-2); (%o4) 1 Is exponent-of broken and the source code comment correct? --Barton