Scalar extension

For a scalar function such as Power (*) there are three obvious ways it can apply to an array argument:

      2 * ⍳6     ⍝ Some powers of 2
1 2 4 8 16 32

      (⍳6) * 2   ⍝ Some squares
0 1 4 9 16 25

      (⍳6) * ⍳6  ⍝ Some self-exponents
1 1 4 27 256 3125

If there's a scalar argument, it has to be used in every function invocation, since there's nowhere else to take arguments from. Rank applies the same principle to arguments with only one cell.