Collecting shells The shells I show in this section are mostly from my fairly small personal collection, obtained at shops and markets around the world. … The Philippines are the largest current source of collectible shells: when molluscs intended as food are caught in nets interesting-looking shells are sometimes picked out before being discarded. Shell collecting as a hobby probably had its greatest popularity in the late 1700s and 1800s.

In Chladni figures of sand on vibrating plates and in cloud streets in the atmosphere what happens is that material collects at points of zero displacement.

As in the note on multilevel formulas below, one can also in effect introduce intermediate variables to get recursive formulas of larger depth, somewhat analogous to results from Collect .

Now collect and rank all the "words" delimited by spaces that are formed.