Infinite Sets. If you continue to study this subject you will find discussions about infinite sets, and the idea of different sizes of infinity. That subject has special names like Aleph-null (how many Natural Numbers), Aleph-one and so on, which are used to measure the sizes of sets.
For decades, glossy paper, the type used in magazines, was made using a white clay called kaolin (named after the Chinese region Kao-Ling where it was mined to produce porcelain).
A3 paper, which is functionally equivalent to tabloid size paper (11 x 17 paper), is appropriate for bi-fold brochures and other full-size presentation or advertising documents. A4 paper, functionally equivalent to letter size paper (8.5 x 11), is the appropriate paper size for correspondence, records, and invoices.