y=: 10 64 100
   ^. y                        NB. Natural logarithm
2.30259 4.15888 4.60517

   10&^. y                     NB. Base ten logarithm
1 1.80618 2

   log=: 10&^. : ^.
   log y
1 1.80618 2

   8 log y
1.10731 2 2.21462

   (^1) log y
2.30259 4.15888 4.60517

   LOG=: 10&$: : ^.            NB. Use of self-reference
   LOG y
1 1.80618 2

   f=: %: : ($:@-)

   (f y),: 100 f y
3.16228 8 10
9.48683 6  0

   ABS=: | : [:

   ABS _4
4

   3 ABS _4
|valence error: ABS
|   3     ABS _4

The domain of the dyad ABS is empty because the domain of [: is empty.