the full yellow sketch in the transparent cellophane bag


In category theory, a faithful functor (respectively a full functor) is a functor that is injective (respectively surjective) when restricted to each set of morphisms that have a given source and target.


Yellow is the color between orange and green on the spectrum of visible light. It is evoked by light with a dominant wavelength of roughly 570–590 nm. It is a primary color in subtractive color systems, used in painting or color printing. In the RGB color model, used to create colors on television and computer screens, yellow is a secondary color made by combining red and green at equal intensity. Carotenoids give the characteristic yellow color to autumn leaves, corn, canaries, daffodils, and lemons, as well as egg yolks, buttercups, and bananas. They absorb light energy and protect plants from photodamage. Sunlight has a slight yellowish hue when sun is near a horizon, due to atmosphere scattering shorter wavelengths (green, blue, and violet).
Because it was widely available, yellow ochre pigment was one of the first colors used in art; the Lascaux cave in France has a painting of a yellow horse 17,000 years old. Ochre and orpiment pigments were used to represent gold and skin color in Egyptian tombs, then in the murals in Roman villas. In the early Christian church, yellow was the color associated with the Pope and the golden keys of the Kingdom, but was also associated with Judas Iscariot and was used to mark heretics. In the 20th century, Jews in Nazi-occupied Europe were forced to wear a yellow star. In China, bright yellow was the color of the Middle Kingdom, and could be worn only by the Emperor and his household; special guests were welcomed on a yellow carpet.
According to surveys in Europe, Canada, and the United States, yellow is the color people most often associate with amusement, gentleness, humor, and spontaneity, but also with duplicity, envy, jealousy, avarice, and, in the U.S., with cowardice. In Iran it has connotations of pallor/sickness, but also wisdom and connection. In China and many Asian countries, it is seen as the color of happiness, glory, harmony and wisdom.


A sketch (ultimately from Greek σχέδιος – schedios, "done extempore") is a rapidly executed freehand drawing that is not usually intended as a finished work. A sketch may serve a number of purposes: it might record something that the artist sees, it might record or develop an idea for later use or it might be used as a quick way of graphically demonstrating an image, idea or principle.
Sketches can be made in any drawing medium. The term is most often applied to graphic work executed in a dry medium such as silverpoint, graphite, pencil, charcoal or pastel. It may also apply to drawings executed in pen and ink, digital input such as a digital pen, ballpoint pen, marker pen, water colour and oil paint. The latter two are generally referred to as "water colour sketches" and "oil sketches". A sculptor might model three-dimensional sketches in clay, plasticine or wax.


In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale (one where the dimensions investigated are much larger than the wavelength of the photons in question), the photons can be said to follow Snell's Law. Translucency (also called translucence or translucidity) allows light to pass through, but does not necessarily (again, on the macroscopic scale) follow Snell's law; the photons can be scattered at either of the two interfaces, or internally, where there is a change in index of refraction. In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction.  Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. The opposite property of translucency is opacity.
When light encounters a material, it can interact with it in several different ways. These interactions depend on the wavelength of the light and the nature of the material. Photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as plate glass and clean water, transmit much of the light that falls on them and reflect little of it; such materials are called optically transparent. Many liquids and aqueous solutions are highly transparent. Absence of structural defects (voids, cracks, etc.) and molecular structure of most liquids are mostly responsible for excellent optical transmission.
Materials which do not transmit light are called opaque. Many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of white light frequencies. They absorb certain portions of the visible spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation. This is what gives rise to color. The attenuation of light of all frequencies and wavelengths is due to the combined mechanisms of absorption and scattering.
Transparency can provide almost perfect camouflage for animals able to achieve it. This is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent.


Cellophane is a thin, transparent sheet made of regenerated cellulose. Its low permeability to air, oils, greases, bacteria, and water makes it useful for food packaging. Cellophane is highly permeable to water vapour, but may be coated with nitrocellulose lacquer to prevent this.
As well as food packaging, cellophane is used in transparent pressure-sensitive tape, tubing and many other similar applications.
Unlike many other similar materials, cellophane is biodegradable. However its manufacture employs toxic chemicals.
"Cellophane" is a generic term in some countries, while in other countries it is a registered trademark.


A bag (also known regionally as a sack) is a common tool in the form of a non-rigid container. The use of bags predates recorded history, with the earliest bags being no more than lengths of animal skin, cotton, or woven plant fibers, folded up at the edges and secured in that shape with strings of the same material.
Despite their simplicity, bags have been fundamental for the development of human civilization, as they allow people to easily collect loose materials such as berries or food grains, and to transport more items than could readily be carried in the hands. The word probably has its origins in the Norse word baggi, from the reconstructed Proto-Indo-European bʰak, but is also comparable to the Welsh baich (load, bundle), and the Greek Τσιαντουλίτσα (Chandulícha, load).
Cheap disposable paper bags and plastic shopping bags are very common in the retail trade as a convenience for shoppers, and are often supplied by the shop for free or for a small fee. Customers may also take their own shopping bags to use in shops. Although, paper had been used for purposes of wrapping and padding in ancient China since the 2nd century BC, the first use of paper bags (for preserving the flavor of tea) in China came during the later Tang Dynasty (618–907 AD).