The operation cdr returns everything in the list except for the first thing.
(cdr '(6))
(cdr '())
Here is a hello world program in Scheme:
Lambda calculus
In mathematical logic and computer science, lambda calculus, also λ-calculus, is a formal system. It was designed to investigate the definition of functions, and how to apply them. It is also a tool for analysing recursion. It was introduced by Alonzo Church and Stephen Cole Kleene in the 1930s. Church used lambda calculus in 1936 to give a negative answer to the Entscheidungsproblem.
Lambda calculus can be used to define what is a computable function. No general algorithm can answer the question of whether two lambda calculus expressions are equivalent. This was the first question, even before the halting problem, for which undecidability could be proved. Lambda calculus has greatly influenced functional programming languages, such as LISP, ML and Haskell.
Lambda calculus can be called the smallest universal programming language. It consists of just one transformation rule (variable substitution) and just one way to define a function. Each "function definition" comes together with a list of the function's parameters, i.e. variables that can be used inside that definition. "Variable substitution" means substitution of values for variables, that is, a transformation step where an application of a function to some arguments is replaced with that function's definition in which all variables (that appear in its list of parameters) are replaced with arguments used in that application.
Lambda calculus is universal in the sense that any computable function can be expressed and evaluated using this formalism. It is thus the same as the Turing machine formalism. However, lambda calculus emphasizes the use of transformation rules. It does not care about the actual machine that implements them. It is an approach more related to software than to hardware.
Family Jewels
Family Jewels is a two disc compilation DVD by the Australian hard rock band AC/DC. It contains videos from the Bon Scott era to the Brian Johnson era. The compilation was released in 2005.
Power transmission
Power transmission is moving energy from where it is made to where it is used.
Power is defined formally as units of energy per unit time.
In SI units: 1 watt = 1 joule/s = 1 newton * metre/second (1W=1J/s=1N·m/s).
With widespread establishment of power grids, power transmission has came to be associated most often with electric power transmission.
Electrical power transmission has replaced mechanical power transmission in all but the very shortest distances. From the start of the industrial revolution until the end of the 19th century mechanical power transmission was the norm. Factories were fitted with overhead driveshafts providing rotary power. Drivebelts would provide power to individual machines on the shop floor.
Mechanical power may be transmitted directly using a solid structure such as a driveshaft; transmission gears can adjust the amount of torque or force vs. speed in much the same way an electrical transformer adjusts voltage vs current.
Chemical energy is transmitted by moving fuels to generate power in distant places. Pipelines and other large infrastructure projects transport natural gas, petroleum and petroleum products for use as fuel.
Ocean surface wave
Ocean surface waves are surface waves that occur in the upper layer of the ocean. They usually result from wind. Some are made by geologic effects like earthquakes or vulcanicity and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis. There is little actual forward motion of individual water particles in an unbroken wave, despite the large amount of energy and momentum it may carry forward. When a wave hits shallow water, it "breaks" because the bottom moves more slowly than the top.
The great majority of large breakers one sees on an ocean beach result from distant winds. Three factors influence the formation of these "wind waves":
All of these factors work together to determine the size and shape of ocean waves. The greater each of the variables, the larger the waves. Waves are measured by:
Waves in a given area typically have a range of sizes. For weather reporting and for scientific analysis of wind wave statistics, their size over a period of time is usually expressed as "significant wave height." This figure represents the average height of the highest one-third of the waves in a given time period (usually twelve hours) or in a specific storm system or event. Given the variability of wave size, the largest individual waves are likely to be twice the reported significant wave height for a particular day or storm.
Crest (physics)
A crest is the point on a wave with the greatest positive value or upward displacement in a cycle. A trough is the opposite of a crest.
When the crest and the trough of two waves of equal magnitude and frequency intersect or collide when in phase with each other the result is called constructive interference and the magnitudes double (above and below the line), when 180° out of phase the result is destructive interference with each other the resulting wave is the undisturbed line that is in the middle of the diagram having zero amplitude.
In other words, the wave crest is called a peak.
Trough
A trough is a box-like drinking vessel for farm animals. Other senses of the word refer to things that are lower than their surroundings, like a trough:
See also trow.
Surface wave
In physics, a surface wave can refer to a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient. For radio waves, a ground wave is a surface wave that propagates close to the surface of the Earth.
Nausea
Nausea is a general feeling of unease and discomfort in the stomach, often with the urge to vomit. The word "nausea" comes from the Latin word for seasickness.
Nausea is a symptom, rather than an illness or disease. The causes for it very often are not in the stomach itself, but somewhere else in the body. Nausea is often caused by a stomach virus. Nausea is usually harmless, in the short term. A good treatment for it can be not to take solid food (and to only drink non-alcoholic drinks, like water). Nausea can also occur during pregnancy, and is quite normal in that context. People can suffer nausea without vomiting.
Anxiety
Anxiety is distress or uneasiness of mind caused by a fear of danger or misfortune. Very often, people with anxiety also feel worries. There can also be physical symptoms, like having a headache or an upset stomach.
Anxiety is a very common human emotion and is often associated with fear, panic, and the fight or flight response. The amount of stress needed to cause anxiety will vary from person to person however, basics include: losing one's job, the death of a loved one, or an accident, to name a few. In most people, anxiety will settle over time and one will return to normal state.
Some people suffer a lot of anxiety over a long period of time which controls them and makes their lives difficult. These conditions are called anxiety disorders and can be treated by therapy and medicine.
General anxiety symptoms are things such as; continual tiredness / exhaustion, inability to relax, lack of confidence, low self-esteem, fear of public places, fear of socializing, frequent feelings of irrational anxiety / fear, compulsive behavior, worrying about making mistakes, regular nightmares, disturbed sleep patterns, excessive crying, headaches, stomach problems, diarrhea, nausea, aching muscles, and so on.