It is my intention to include here other features of the early versions of J, as illustrated in my talk on *The story of APL & J *, at the J Conference, Toronto, October 2000

A crucial early step leading to the creation of the J language was Ken Iverson‘s chance acquisition of a second-hand copy of March & Wolff‘s *Calculus*, 1st Edition, 1917. Click here to display p.43, 57, 58
*The sum, product, & quotient of two functions*
(56KB)

i.e. (u + v) y is (u y) + (v y) and, by extension, x (u + v) y is (x u y) + (x v y)

This construction, which was introduced in the first version of J (1990), was invalid in APL.
It is fully implemented in J as the *fork* and the related *hook* – the composition of two functions.

See:

Iverson, Kenneth E. and E. E. McDonnell, Phrasal Forms. Conference Proceedings APL89, ACM, New York, APL Quote Quad, vol.19, no 4, p.197-199.

Hui, Roger K.W., K.E. Iverson, E.E. McDonnell, Tacit Programming, APL91 Conference, Stanford, CA, Proceedings, APL Quote Quad, vol.21, no.4, p.202-211, ACM, New York