- First, a the function extracting its argument's initial element in ravel order.
- Mix, a function combining its argument's elements (requiring conforming shapes or padding with fill elements).
Early experiments in array nesting usually defined a primitive to extract the contents of a nested scalar, but did not always specify how it should behave on an array. Jim Brown's "A Generalization of APL", stated that it "may be undefined" on non-scalar arrays. However, all dialects do define it on non-scalars, but with differing definitions.