They highlight what I would call a limitation in other array languages. Octave (and I would expect MATLAB as well) allows scalar operators to be lifted to multi

They highlight what I would call a limitation in other array languages. Octave (and I would expect MATLAB as well) allows scalar operators to be lifted to multidimensional arrays only if one operand is scalar or both have the same dimensionality, which looks to a J programmer like it's just incomplete special-casing. By comparison, J's lifting permits mismatched dimensionality ("rank"), e.g. using a scalar operator on a list and a matrix, though the dimensions of the particular axes ("shapes" of the arrays) must still match (one must be a prefix of the other). This generalizes to operators written for higher-rank arrays too.