Category: knowledge

Create lengthy password using cryptographics hash software

If you can remember only easy to remember password then this method can help creating a strong password

For this you will require VSCryptoHash  software. Download and install it.

VSCryptoHash Download link  :


What you need to remember

  1. An easy password that you can remember
  2. The type of hash used : SHA-3 (512-bit)



Here i have used easy to remember password : tomahawkmissile

Hash type :  SHA-3 (512-bit)

  • Select SHA-3 (512-bit) as hash type.
  • Enter the easy password in Input data as text
  • Click “calculate hash”
  • As you can see below a lengthy  “HEX Hash value (SHA3 (512)) ” has been calculated



Now you can use this lengthy hash value as password instead of easy password “tomahawkmissle”

Lengthy password   6BC4D708E041136BE68766FDA7A8272193BBA11394AD70693A06C7CB9D327E6BD495EEE6E6B166BAF30F1EAF5C046FBB5053B26CD4FF54EA2807A22D8C020C87

this 128 character long password. So anyone trying to crash this lengthy password will fail.


2)  Use other hash algorithm

Instead of SHA 3 (512-bit)  you can use other hash algorithm also.




  • Depending on the hash algorithm you use, the output HEX hash value size will change.










3)  Creating lengthy password using iterating the hash

What you need to remember

  • An easy password that you can remember
  • The type of hash used : SHA-3 (512-bit)
  • The number of times you iterated



  • Easy to remember password : tomahawkmissle
  • Hash type :  SHA-3 (512-bit)
  • The number of times to iterate  :  4


Iteration number 1

  • Set Input data as text : tomahawkmissle
  • Set hash type : SHA-3 (512-bit)
  • Click “calculate hash” to create a hash value
  • Click “copy hash value” next to the HEX hash value to copy the password in clipboard

Lenghty password generated  :  6BC4D708E041136BE68766FDA7A8272193BBA11394AD70693A06C7CB9D327E6BD495EEE6E6B166BAF30F1EAF5C046FBB5053B26CD4FF54EA2807A22D8C020C87



Iteration no. 2

  • Use the previously generated HEX hash value as “input data as text”
  • Click “Clear entered data” to clear all the data
  • Paste the copied previous HEX value in the “input data as text”
  • Click “calculate hash” to generate fourth Hex Hash Value
  • Click “copy hash value” next to the HEX hash value to copy the password in clipboard

Lenghty password generated  :  646A3BC18DA8A73B8461F52138AFC01C3F8F7300F14AC0A9273C1648113AF5807143EDA8E42C9FE870090F6B2964D6C0BEF1F9D3A56082B6DA5BC06473BC5A5D



Iteration no. 3

  • Use the previously generated HEX hash value as “input data as text”
  • Click “Clear entered data” to clear all the data
  • Paste the copied previous HEX value in the “input data as text”
  • Click “calculate hash” to generate fourth Hex Hash Value
  • Click “copy hash value” next to the HEX hash value to copy the password in clipboard

Lenghty password generated  :    C8D0733DB68928E7EC22B2AD5298CAE27ED3FF924A4B4D4FD78554BEDE8B70CCC1392E2224408AFC4D5B5AF935584CE875F95E5B0D1A5990803C2A82A5AE54F2



Iteration no. 4

  • Use the previously generated HEX hash value as “input data as text”
  • Click “Clear entered data” to clear all the data
  • Paste the copied previous HEX value in the “input data as text”
  • Click “calculate hash” to generate fourth Hex Hash Value
  • Click “copy hash value” next to the HEX hash value to copy the password in clipboard

Lenghty password generated  :  571AEE3F20C70360FB3CDB2A226D78ED9EC02E314187EC5E733CD15E77C92B947BF53E46E38B200589D2C941705A5FFF573EFFC53A9258A91B2B8A625CA4FFC9


Now that four iterations are over, you can use the fourth HEX hash value as lengthy generated password which is 571AEE3F20C70360FB3CDB2A226D78ED9EC02E314187EC5E733CD15E77C92B947BF53E46E38B200589D2C941705A5FFF573EFFC53A9258A91B2B8A625CA4FFC9


 4) You can use tricks to make it even more difficult to for someone to guess the password

You may use various tricks. But just don’t forget what trick you have used or else you won’t be able to recover the lengthy password.

Use may use only part of the lengthy password

  • Example : You may use only “AE6AD23F446310D777C25300EF14BF2C7939F2505B63A4E46ED98CF498F513E274EA99E48632DB” as password instead of whole HEX hash value by cutting out “CAFA0CE29D7E5DDACAB1ED2A6A732778EED71C14CE4CD9E301” from it.


You may combine two or more algorithm

You may two or more hash algorithm to create a final lengthy password.

Do not forget the order in which you used the has algorithm

Example :  I am using two hash algorithm

  2. SHA 3(512-bit)
  • First WHIRLPOOL (512-bit) has been used


  • Second SHA-3 (512-bit) is used
  • use the previously calculated HEX hash value as “input data as text”
  • Finally calculated HEX hash value to be used a lengthy password :    4AA94A7927B24A6D0EA0A96903E0FF8C4190A6FBE3B51965A213CEE1FC92333CD696AB3D0BF97B974F1BC17CA18170AE12EF08E6AA90D92BD8E8720A1A46F713





How to keep your desktop or laptop computer fast and safe from all forms of threat

A personal computer is very helpful to anyone. But threats from malware can make it very slow and compromise your personal data. So you must install a antivirus in the computer and update all the software regularly.

1. First to consider is the Operating system. The newest operating system is the best because it supports newest hardware and is most likely to be free from software vulnerabilities.

In terms of Operating system most preferred is

  1. Windows 8
  2. Windows 7
  3. Windows XP

In case of Windows 8 and 7 install 64 bit version of OS because most processor supports 64 bit instruction.

In case of Windows XP install 32 bit Windows XP service pack 3

In case of Windows 7 install Windows 7 SP 1

In case of Windows 8 install Windows 8.1

2. Once Operating System installation is complete. Download and install the latest drivers for the computer. Keep in mind that 64 bit OS would require a 64 bit version of the driver and 32 bit OS requires a 32 bit version of driver.

Important drivers would include chipset, video, audio, LAN, WLAN and bluetooth driver.



Windows Xp 64 bit

Windows XP 32 bit

Windows Vista/7/8  64 bit

Windows Vista/7/8  32 bit

AMD Catalyst driver

Windows Xp 64 bit

Windows XP 32 bit

Windows Vista/7/8  64 bit

Windows Vista/7/8  32 bit

3. Keep your operating system updated by turning on automatic update.

4. Install Internet Security software. It protects the computer from all kinds of malware and internet originated threats. Also it must not cause any stability issue with other software’s installed in the system. It must not cause blocking of internet access.

Best paid internet security vendors are –

  1. kaspersky – kasperky is heavy on system resources but provides very high level of security. Easy to use and highly configurable.
  2. F Secure – f secure is very light on system resources and provides very high level of security. Easy to use. Less configurable.
  3. ESET Smart Security – Light on system resources . provides very high level of security. Easy to use.
  4. Emsisoft Internet Secuirty – Provides very high level of security. generates a lot of popups. So good only for tech savvy people
  5. Bullguard – provides very good level of security and can be used by less tech savy users. Highly configurable. easy to use.

Search in ebay to get low price internet security software.

Check here to get at low price

Best free antivirus vendors are –

  1. 360 Internet security (Qihoo) – Easy to use. moderatly configurable. Requires some computer knowhow. Very high level of security.
  2. Bitdefender antivirus free – Very easy to use. less configuarable . very high security.
  3. Comodo internet security –  only for tech savvy. Highly configurable. High security.
  4. Avast – very easy to use. highly configurable. Provides less security than those above.
  5. Avira –
  6. AVG

Bitdefender and 360 internet securirty recommended.

DOWNLOAD free antivirus

5. The software you install must be latest so that it is free from vulnerabilities and bugs. The newest versions are most secure.

Using cracked software is one of the main reason people get infected with malwares. Most of the cracked software available in internet contains malware. This does not mean that there aren’t geniunly cracked software out there. One way to keep your computer safe is to upload the crack to . This website will tell you if the file is infected with malware or not.

Second reason to get infected is surfing websites that contains malicious scripts or codes. Just by visiting these websites you computer can get infected. Using good internet security software protects from these malicious websites.

6. Use Web Browsers like chrome and Firefox. These are constantly updated so that vulnerabilities and bugs are fixed. So always use the latest version. Also Firefox and Chrome protects from some malicious url and phishing websites. This adds extra layer of protection.

Also most Antivirus or internet security software’s support Chrome and Firefox. So you will be protected from web treats.



7. Install web browser addons like Adblock Plus and WOT. These adds extra layer of protection to the computer.

Many times ads are very intrusive. These ad banner may mislead viewers into installing malwares. They may trick you into giving personal information by claiming that you have won something big. They may lead you to websites that contains malicious codes.

DOWNLOAD AdBlock plus


8. For video and audio player download from following locations –

I suggest you use AIMP 3 as audio player

Media Player Classic Home Cinema as video player.

9.  If you use file sharing software then download from locations below

I recommend using utorrent for downloading torrent files.

DOWNLOAD utorrent

10. For Download manager/accelerator use Free download manager


FDM may not integrate with chrome browser.

11. For PDF reader application choose from Foxit reader and Adobe reader

DOWNLOAD Foxit Reader

DOWNLOAD Adobe Reader

12. For Office works like spreadsheet, Word and presentation use Kingsoft Office free

DOWNLOAD Kingsoft Office free

Alternate Libre office

13. For File archiver used for compressing and decompressing file download from

Use bandizip

14. For system information use



15. For system cleaning and tweaking


WiseCare 365

Advanced system care

16. For Disk Defragment software use

Smart Defrag

17. For codec pack

K-Lite Codec Pack

18. For image viewer use


19. For image editing use

The Gimp

20. For network speed and bandwidth monitor use


21. For Emulate virtual CD/DVD-ROM/HD DVD and Blu-ray drives and creating disk images

DAEMON Tools Lite

22. Install Essential Packages

Create a strong password that are easy to remember

A strong password is must to provide strong security to your online login credential. But the problem is the strongest password is difficult to remember. Also using simple password is not good because it can be cracked very easily. The more long a password is the more strong it is.


  • Combine many words and numbers to many a long and strong password. Like combine “Callofduty” , “mercedes“, “ihopethisisstrongpassword” to make a long password “Callofdutymercedesihopethisisstrongpassword“. Also add a number to it if possible. Like add “64890” to get “Callofdutymercedesihopethisisstrongpassword64890“. All the words and numbers are easy to remember and when combined creates very strong password. The more difficult the word the more difficult it gets to guess it. Like one can easily guess that you may have used words like “callofduty” and “mercedes” because these are famous games and brand. So use less popular words and sentences. You may use quotes to make strong password. Like “If something sounds too good to be true it is probably false.”
  • Make you password more difficult to guess. By changing words “callofduty” to “CaLlOfDuTy” you can make it more difficult to guess. Odd letters are in capital. Thus making “Callofdutymercedesihopethisisstrongpassword64890” to “CaLlOfDuTyMeRcEdEsIhOpEtHiSiSsTrOnGpAsSwOrD64890
  • You may also go like this by changing words “callofdutyihopethisisstrongpassword” to “CALLofDUTYiHOPEthisISstrongPASSWORD“.
  • You may also change words like this by repeating letter to specified no of times. Change “callofduty” to “ccccaaaallllooooffffdddduuuuttttyyyy“.
  • You may repeat letters in words in increasing fashion. Change “callofduty” to “caallloooofffffdddddduuuuuuuttttttttyyyyyyyyy
  • You may also repeat numbers to specified times. Like change “84790” to “888444777999000“.
  • You may repeat numbers in increasing fashion. Like change “84790” to “844777999900000
  • You may mix numbers and words. Like mix “callofduty” to “84790” to create “c8a4l7l9o0fduty“.
  • Use some letters of phrases and quotes. Like from “If something sounds too good to be true it is probably false” take first letter of every word which makes “isstgtbtiipf“.
  • Use symbols instead of number. Replace number “84790” with symbols “*$&()” which correspond to that number in keyboard.
  • Play more with keyboard. Replace number with symbols before or after that number. replace number “84790” with symbol before that number “&#^*(” or with symbol after that number “(%8)_“.
  • Just repeat the word. Repeat word “mercedes” to “mercedesmercedesmercedesmercedes” .

A good password is required to have letters in both lower and upper case, numbers and symbols. Also the length must be large than 12 characters.

Say I can remember only “mercedes” and number “87402“. I change “mercedes” to “MeRcEdEs“,  and get symbol associated with number before “87402” which is “&^#(!“. Thus making final password “MeRcEdE87402&^#(!” which is difficult to guess or crack.


Rare Earth Elements and their Uses

What Are Rare Earth Elements (REEs)?

Rare earth elements are a group of seventeen chemical elements that occur together in the periodic table (see image at right). The group consists of yttrium and the 15 lanthanide elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). Scandium is found in most rare earth element deposits and is sometimes classified as a rare earth element.

The rare earth elements are all metals and the group is often referred to as the “rare earth metals”. These metals have many similar properties and that often causes them to be found together in geologic deposits.

Some researchers do not consider scandium to be a rare earth element, however the International Union of Pure and Applied Chemistry includes scandium in their rare earth element definition.

Uses of Rare Earth Elements

Rare earth metals and alloys that contain them are used in many devices that people use every day such as: computer memory, DVD’s, rechargeable batteries, cell phones, car catalytic converters, magnets, fluorescent lighting and much more.

During the past twenty years there has been an explosion in demand for many items that require rare earth metals. Twenty years ago there were very few cell phones in use but the number has risen to over 5 billion in use today. The usage of computers and DVDs has grown almost as fast as cell phones.

United States Usage
(2008 data)
Metallurgy & alloys
Chemical Catalysts
Phosphors for monitors, television, lighting
Catalytic converters
Glass polishing
Permanent magnets
Petroleum refining

Many rechargeable batteries are made with rare earth compounds. Demand for the batteries is being driven by demand for portable electronic devices such as cell phones, readers, computers and cameras.

Several pounds of rare earth compounds are in batteries that power electric vehicles and hybrid-electric vehicles. As concerns for energy independence, climate change and other issues drive the sale of electric vehicles the demand for batteries made with rare earth compounds will climb even faster.

Rare earths are used as catalysts, phosphors and polishing compounds. These are used for air pollution control, illuminated screens on electronic devices and optical-quality glass. All of these products are expected to experience rising demand.

Other substances can be substituted for rare earth elements in their most important uses, however, these substitutes are usually less effective and costly.

From the 1950s until the early 2000s cerium oxide was a very popular lapidary polish. It was inexpensive and very effective. The recent price increases have almost eliminated the use of cerium oxide in the lapidary arts.

Major Uses of Rare Earth Elements

Lanthanum comes from the mineral bastnasite, and is extracted via a method called “solvent extraction.” Lanthanum is a strategically important rare earth element due to its activity in catalysts that are critical in petroleum refining. By one estimate, lanthanum “cracking-agents” increase refinery yield by as much as 10%, while reducing overall refinery power consumption.

Cerium is the most abundant of the rare earth elements. Cerium is critical in the manufacture of environmental protection and pollution-control systems, from automobiles to oil refineries. Cerium oxides, and other cerium compounds, go into catalytic converters and larger-scale equipment to reduce the sulfur oxide emissions. Cerium is a diesel fuel additive for micro-filtration of pollutants, and promotes more complete fuel combustion for more energy efficiency.

Neodymium is a critical component of strong permanent magnets. Cell phones, portable CD players, computers and most modern sound systems would not exist in their current form without using neodymium magnets. Neodymium-Iron- Boron (NdFeB) permanent magnets are essential for miniaturizing a variety of technologies. These magnets maximize the power/cost ratio, and are used in a large variety of motors and mechanical systems.

Europium offers exceptional properties of photon emission. When it absorbs electrons or UV radiation, the europium atom changes energy levels to create a visible, luminescent emission. This emission creates the perfect red phosphors used in color televisions and computer screens around the world. Europium is also used in fluorescent lighting, which cuts energy use by 75% compared to incandescent lighting. In the medical field, europium is used to tag complex biochemical agents which helps to trace these materials during tissue research.

Praseodymium comprises just 4% of the lanthanide content of bastnasite, but is used as a common coloring pigment. Along with neodymium, praseodymium is used to filter certain wavelengths of light. So praseodymium finds specific uses in photographic filters, airport signal lenses, welder’s glasses, as well as broad uses in ceramic tile and glass (usually yellow). When used in an alloy, praseodymium is a component of permanent magnet systems designed for small motors. Praseodymium also has applications in internal combustion engines, as a catalyst for pollution control.

Yttrium is rare in bastnasite, so is usually recovered from even more obscure minerals and ores. Still, almost every vehicle on the road contains yttriumbased materials that improve the fuel efficiency of the engine. Another important use of yttrium is in microwave communication devices. Yttrium- Iron-Garnets (YIG) are used as resonators in frequency meters, magnetic field measurement devices, tunable transistors and Gunn oscillators. Yttrium goes into laser crystals specific to spectral characteristics for high-performance communication systems.

Other Rare Earth Elements

Most of the remaining lanthanides fall into the group known as the “heavies” and include: Samarium, Gadolinium, Dysprosium, Terbium, Holmium, Erbium, Thulium, Ytterbium, and Lutetium.

Samarium has properties of spectral absorption that make it useful in filter glasses that surround neodymium laser rods.

Gadolinium offers unique magnetic behavior. Thus this element is at the heart of magneto-optic recording technology, and other technology used in handling computer data.

Dysprosium is a widely used rare earth element that helps to make electronic components smaller and faster.

Terbium is used in energy efficient fluorescent lamps. There are various terbium metal alloys that provide metallic films for magnetooptic data recording.

Holmium is exceedingly rare and expensive. Hence it has few commercial uses.

Erbium has remarkable optical properties that make it essential for use in long-range fiber optic data transmission.

Thulium is the rarest of the rare earth elements. Its chemistry is similar to that of Yttrium. Due to its unique photographic properties, Thulium is used in sensitive X-ray phosphors to reduce X-ray exposure.

Ytterbium resembles Yttrium in broad chemical behavior. When subject to high stresses, the electrical resistance of the metal increases by an order of magnitude. So ytterbium is used in stress gauges to monitor ground deformations caused, for example, by earthquakes or underground explosions.

Lutetium, the last member of the Lanthanide series is, along with thulium, the least abundant. It is recovered, by ion-exchange routines, in small quantities from yttrium-concentrates and is available as a high-purity oxide. Cerium-doped lutetium oxyorthosilicate (LSO) is currently used in detectors in positron emission tomography (PET).

Did You Know? Tiny amounts of rare earth metals are used in most small electronic devices. These devices have a short life-span and REE recycling is infrequently done. Billions are thrown away each year. Image © Bakaleev Aleksey, iStockphoto.

Critical Defense Uses of Rare Earth Elements

Rare earth elements play an essential role in our national defense. In the Gulf Wars, night-vision goggles, precision-guided weapons and other defense technology gave the United States military a tremendous advantage. Rare earth metals are key ingredients for making the very hard alloys used to make armored vehicles and projectiles that shatter upon impact in thousands of sharp fragments.

Substitutes can be used for rare earth elements in some defense applications, however, those subsitutes are not as effective and that will diminish military superiority. Several uses of rare earth elements are summarized in the table below (5).

Defense Uses of Rare Earth Elements
Lanthanum night-vision goggles
Neodymium laser range-finders, guidance systems, communications
Europium fluorescents and phosphors in lamps and monitors
Erbium amplifiers in fiber-optic data transmission
Samarium pernament magnets that are stable at high temperatures
Samarium precision-guided weapons
Samarium “white noise” production in stealth technology

Are These Elements Really “Rare”?

Rare earth elements are not as “rare” as their name implies. Thulium and lutetium are the two least abundant rare earth elements – but they each have an average crustal abundance that is nearly 200 times greater than the crustal abundance of gold (1). However, these metals are very difficult to mine because it is unusual to find them in concentrations high enough for economical extraction.

The most abundant rare earth elements are cerium, yttrium, lanthanum and neodymium (2). They have average crustal abundances that are similar to commonly used industrial metals such as chromium, nickel, zinc, molybdenum, tin, tungsten and lead (1). Again, they are rarely found in extractable concentrations.

Rare Earth Element Mine Production and Trade

Significant amounts of rare earth elements are produced in only a few countries. China is the dominant producer of rare earth elements and is believed to be responsible for over 95% of the world mine production on a rare earth oxide equivalent basis. Other countries with notable production in 2009 were: Brazil, India, Kyrgyzstan and Malaysia. Minor production may have occurred in Indonesia, Commonwealth of Independent States, Nigeria, North Korea and Vietnam (3). The United States Geological Survey reports that significant exploration and new mining activity is expected from Canada and Australia (3).

World Mine Production and Reserves (2009 Data)
Country Production (Metric Ton) Reserves (Metric Ton)
United States
Commonwealth of Independent States
not available
Other countries
not available
World total (rounded)

China’s World Production Dominance

China became the world’s dominant producer of rare earth elements in the early 1990s, when production at the Mountain Pass mine in California began to decline. China’s dominance increased rapidly and in 2000 China accounted for about 90% of world rare earth production. China sold rare earths at such low prices that the Mountain Pass mine and others throughout the world were unable to compete.

In early 2010 China accounted for over 95% of the world’s rare earth production. China is also the dominant consumer of rare earth elements, used mainly in manufacturing electronics products for domestic and export markets. Japan and the United States are the second and third largest consumers of rare earth materials.

In 2010 China announced that they would significantly restrict their rare earth exports to ensure a supply for domestic manufacturing. This announcement triggered some panic buying and rare earth prices shot up to record high levels.

Chinese companies have also been seeking rare earth properties in other countries. For example: in 2009 China Non-Ferrous Metal Mining Company bought a majority stake in Lynas Corporation, an Australian company that has one of the highest outputs of rare earth elements outside of China.

The Dangers of a Dominant World Producer

Supply and demand normally determine the market price of a commodity. As supplies shrink prices go up. As prices go higher those who control the supply are tempted to sell and entrepreneurs start developing new sources of supply.

With rare earth elements the time between an entrepreneur’s decision to acquire a property and the start of production can be several years or longer. There is no quick way to increase supply.

If a single country controls almost all of the production and makes a firm decision not to export then the entire supply of a commodity can be quickly cut off. That is a dangerous situation when new sources of supply take so long to develop.

World Rare Earth Mineral Resources

“Rare earths are relatively abundant in the Earth’s crust, but discovered minable concentrations are less common than for most other ores. U.S. and world resources are contained primarily in bastnäsite and monazite. Bastnäsite deposits in China and the United States constitute the largest percentage of the world’s rare-earth economic resources, while monazite deposits in Australia, Brazil, China, India, Malaysia, South Africa, Sri Lanka, Thailand, and the United States constitute the second largest segment. Apatite, cheralite, eudialyte, loparite, phosphorites, rare-earth-bearing (ion adsorption) clays, secondary monazite, spent uranium solutions, and xenotime make up most of the remaining resources. Undiscovered resources are thought to be very large relative to expected demand.” Quoted from the United States Geological Survey’s Mineral Commodity Summary .

Large undeveloped deposits of rare earth minerals are known to occur in China. Significant deposits are also known in Australia. Exploration is identifying new deposits in Canada and the United States.

Rare Earth Element Outlook

“Rare-earth use in automotive pollution control catalysts, permanent magnets, and rechargeable batteries are expected to continue to increase as future demand for conventional and hybrid automobiles, computers, electronics, and portable equipment grows. Rare-earth markets are expected to require greater amounts of higher purity mixed and separated products to meet the demand. Demand for cerium and neodymium for use in automotive catalytic converters and catalysts for petroleum refining was expected to expand by 6% to 8% per year for the next 5 years if the world economy remains strong.
Rare-earth magnet demand was expected to increase by 10% to 16% per year through 2012, increasing to 45,000 t to 50,000 t by 2012 (Kingsnorth, 2008). Future growth was expected for rare earths in rechargeable NiMH batteries, especially those used in hybrid vehicles, increasing to 10,000 t to 20,000 t REO by 2012. NiMH demand was also expected to increase (moderated by increasing demand for lithium-ion batteries) with increased use in portable equipment, such as camcorders, cellular telephones, compact disk players, digital cameras, digital video disk players, laptop computers, and MPEG audio-layer-3 players.

Increased rare earth use was expected in fiber optics, medical applications that include dental and surgical lasers, magnetic resonance imaging, medical contrast agents, medical isotopes, and positron emission tomography scintillation detectors. Future growth potential was projected for rare-earth alloys employed in magnetic refrigeration (Gschneidner and Pecharsky, 2008).” Quoted from the United States Geological Survey Minerals Yearbook .

Refrences :