Air Coryell

Last updated

In American football, Air Coryell is the offensive scheme and philosophy developed by former San Diego Chargers coach Don Coryell. The offensive philosophy has been also called the "Coryell offense" or the "vertical offense". [1]

Contents

With Dan Fouts as quarterback, the San Diego Chargers' offense was among the greatest passing offenses in National Football League history. The Chargers led the league in passing yards an NFL record six consecutive years from 1978 to 1983 [2] and again in 1985. They also led the league in total yards in offense from 1978 to 1983 and in 1985. Dan Fouts, Charlie Joiner, and Kellen Winslow would all be inducted into the Pro Football Hall of Fame from those Charger teams.

Pre-Coryell NFL

Before Coryell, NFL teams generally used the pro set formation [3] in ball-control, grind-it-out-style offenses that used play-action fakes to set up deep passing attempts when defenses stacked up vs the running game. The pro set features a tight end, two wide receivers, a halfback, and a fullback, often split behind the quarterback. On pass plays, the pro set provided one or even two backs to help protect the quarterback. QBs generally took snaps from under center to allow for more effective use of the play action pass. [4]

In 1978, the contact from defenders on receivers was minimized with the passing of the Mel Blount Rule, which prohibited defenders from making contact with receivers past five yards from the line of scrimmage. [5] [6]

Coryell opens up passing in the NFL

After Coryell arrived in the NFL from jobs with college football teams, he set the league on its ear with his passing offenses. He won two consecutive division titles (1974–1975) with the St. Louis Cardinals, whose offense emphasized the pass while running the standard pro set. [7] Coryell moved to the Chargers and reached the playoffs in four consecutive seasons that included three straight division titles (1979–1982). The Chargers in 1979 were the first AFC Western Division champion to run more passing plays (541) than rushing (481). [8] Coryell's Chargers teams led the league in passing in seven of eight years. [9] The Pro Football Hall of Fame called the Chargers' offenses under Coryell "one of the most explosive and exciting offenses that ever set foot on an NFL field." [10] Coryell was the first coach to win more than 100 games at both the collegiate and professional level. Coryell's offensive innovations changed the entire nature of the league from a run-first league to a pass-first one.

As of 2022, most NFL offenses' passing games are based at least partially on Coryell conventions.

Mike Martz, who ran The Greatest Show on Turf with the St. Louis Rams, said, "Don is the father of the modern passing game. People talk about the West Coast offense, but Don started the 'West Coast' decades ago and kept updating it. You look around the NFL now, and so many teams are running a version of the Coryell offense. Coaches have added their own touches, but it's still Coryell's offense. He has disciples all over the league. He changed the game". [11]

Attributes of Air Coryell

The Coryell offense is based on Sid Gillman's offense that required the defense to defend the entire field. [6] The passing game was based on timing and rhythm, and coaching the system required a lot of repetition. [12] Coryell expanded on those principles by putting receivers in motion. With the new defensive rules limiting contact to near the line of scrimmage, receivers in motion would be virtually impossible to jam. Coryell not only placed wide receivers in motion, he did so with tight ends and running backs as well. Putting the players in motion also had the advantage of allowing the quarterback to determine pre-snap if the defense would be playing zone or man-to-man defense. [6] It was easier to read the coverage before the snap than afterwards due to the pass rush. [12] It is also harder for a defender to cover if he has to change direction with the receiver instead of squaring up and getting set before a play. Defenses that react to the motion could get confused, leaving a defender in the wrong position. [13]

The offense did not have any set formations, as receivers could line up anywhere on any given pass play. [6] Passes were thrown to a spot before the receiver even got there, allowing defenders no hint where the pass was being targeted. [14] Each receiver had two or three different route options they could adjust depending on the coverage during the play. [15] Throwing a deep pass was the first option on each play. [12] Coryell's offense had more progressions than Gillman's, with backup options for screen passes and underneath routes. [16]

The Coryell offense is a combination of deep and mid range passing and power running. [17] The offense relies on getting all five receivers out into patterns that combined stretched the field, setting up defensive backs with route technique, and the quarterback throwing to a spot on time where the receiver can catch and turn upfield. Pass protection is critical to success because at least two of the five receivers will run a deep in, skinny post, comeback, speed out, or shallow cross.

Overall, the goal of the Coryell offense is to have at least two downfield, fast wide receivers who adjust to the deep pass very well, combined with a sturdy pocket quarterback with a strong arm. The Coryell offense uses three key weapons. The first is a strong inside running game, the second is its ability to strike deep with two or more receivers on any play, and the third is to not only use those two attacks in cooperation with each other, but to include a great deal of mid-range passing to a TE, WR, or back.

The Coryell offense introduced the concept of a tight end that ran wide receiver-type routes with Kellen Winslow in 1980. [18] Tight ends previously were primarily blockers lined up next to an offensive lineman and ran short to medium drag routes. [19] Winslow was put in motion so he would not be jammed at the line, or he was lined up wide or in the slot against a smaller cornerback. [18] Former Chargers assistant coach Al Saunders said Winslow was "a wide receiver in an offensive lineman's body." [19] Back then, defenses would cover Winslow with a strong safety or a linebacker, as zone defenses were not as popular. [20] Strong safeties in those times were almost like another linebacker, a run defender who could not cover a tight end as fast as Winslow. Providing another defender to help the strong safety opened up other holes. [21] Head coach Jon Gruden called Winslow the first "joker" in the NFL. He could line up unpredictably in any formation from a three-point stance as a blocker to a two-point stance or being in motion as a receiver. [22]

After the Chargers in 1980 acquired running back Chuck Muncie, the offense started using a single set back featuring Muncie as the lone running back and adding a second tight end into the game. When defenses countered with extra defensive backs, the offense would run the ball. Joe Gibbs, the Chargers offensive coordinator at the time, said that marked "the evolution of the one-back offense." [23]

Gibbs served as head coach of the Washington Redskins from 1981-1992, and during that time, he won three Super Bowls with a Coryell offense. [24] His offense featured a smash mouth running game with 3 different running backs, Hall of Famer John Riggins, George Rogers and Earnest Byner, behind a massive offensive line known as the "Hogs." Gibbs's offense also showcased a 3-receiver deep air attack featuring Hall of Famer Art Monk, Gary Clark and Ricky Sanders, known as "The Posse." Gibbs usually kept the tight end in as an extra blocker, especially to neutralize pass rushing specialist and Hall of Fame linebacker Lawrence Taylor of the New York Giants. Today, many Coryell offenses still reduce the use a tight end, except in the red zone,[ citation needed ].

Gibbs, who earned induction into the Pro Football Hall of Fame for his work as Redskins head coach, is also the first head coach in NFL history to win 3 Super Bowls with 3 different quarterbacks: Joe Theismann, Doug Williams, and Mark Rypien. Gibbs also coached the Redskins from 2004-2007, but was unable to duplicate the success he enjoyed during his first term in Washington.

Norv Turner, a former Washington Redskins and San Diego Chargers head coach, and offensive coordinator for many NFL teams (most notably for the Dallas Cowboys during the early 1990s), also implemented a version of the Coryell style of offense. The Turner strain of Coryell offenses are still very reliant on a good receiving TE. Norv Turner strains sometimes feature an 'F-Back' (formerly known as an 'H-Back' in the 1980s), a hybrid tight end/wide receiver/fullback/running back. An F-Back is a multi-purpose, unpredictable tool for the offense. On any play he may carry the ball, lead block or pass block, play as a wide receiver, or run a tight end route. He is also part decoy, as his unpredictable role forces defenses to keep an eye on him, thereby opening up other opportunities for the offense.[ citation needed ].

History of the name

Originally it was known as the West Coast offense until an article about San Francisco 49ers Head Coach Bill Walsh in Sports Illustrated in the early 80s incorrectly called Walsh's offense "the West Coast offense," and this mis-labelling stuck. Subsequently, Coryell's offense scheme was referred to as "Air Coryell"—the name announcers had assigned to his high powered Charger offenses in San Diego, featuring 3 Hall of Famers in QB Dan Fouts, WR Charlie Joiner, & TE Kellen Winslow, [25] as well as Pro Bowl WR Wes Chandler & HB Chuck Muncie. Today it is also known as the "Coryell offense", although the "vertical offense" is another accepted name.

Disciples of Air Coryell

In NFL coaching circles, the most famous and successful advocates of the Air Coryell system are Norv Turner, Mike Martz and Al Saunders.

Norv Turner's version

Norv Turner first learned the offense from longtime Coryell assistant Ernie Zampese. [26] As offensive coordinator with the Dallas Cowboys, Turner ran Coryell's offense with a greater emphasis on sideline throws than the Chargers used. [24] Turner's take on the Coryell system turned around the career of Hall of Fame QB Troy Aikman, and has also proven to be very successful with talented high draft picks struggling with the complexities of the NFL, such as Alex Smith. Turner's variant is not the most robust flavor of the Air Coryell offense. It is a very sound, QB friendly scheme that favors taking controlled chances, like quicker midrange post passes to WRs off play action rather than slower developing passes that leave QBs exposed. It is almost exclusively run out of the pro set. Turner favors a more limited palette of plays than Coryell and most other Coryell disciples, instead insisting on precise execution. His offenses are usually towards the top of the league standings, but are often labeled predictable. His offenses tend to include a strong offensive line, a strong running game, a #1 WR who can stretch the field and catch jump balls in the end-zone, a good receiving TE to attack the space the WRs create in the middle of the field and a FB who fills the role of a lead blocker and a final option as an outlet receiver. [27] In Dallas, Turner helped make RB Emmitt Smith & WR Michael Irvin Hall of Famers, and TE Jay Novacek a five time Pro Bowler.

As offensive coordinator of the Cowboys under head coach Jimmy Johnson, Norv Turner enjoyed great success, piloting Dallas to back-to-back Super Bowl titles in 1992 and 1993. His record as a head coach, however, has only seen limited results. Turner first served as head coach of the Washington Redskins from 1994-2000, but the team only made the playoffs once, in 1999. He also served as head coach of the Oakland Raiders from 2004-2005, but endured 2 more losing seasons. Turner did, however, enjoy a good amount of success as San Diego Chargers head coach from 2007-2012. During his time with the Chargers, Turner's system helped quarterback Philip Rivers set new franchise records for single-season quarterback rating and touchdown passes in 2008. Besides Rivers, the Chargers featured a strong running game, starring Hall of Fame RB LaDainian Tomlinson. Turner's offense also had a potent passing game, which featured multiple-time Pro Bowl TE Antonio Gates. San Diego won 3 straight AFC West division titles, from 2007-2009. However, despite having one of the NFL's most talented rosters, Turner was never able to guide the Chargers to the Super Bowl. Norv Turner also owns the rather dubious distinction of having the most career wins of any NFL head coach with a career losing record, compiling an overall record of 118-126-1 (.484), regular season and playoff games combined.

Mike Martz's version

The Mike Martz variant was a much more aggressive passing offense, frequently deploying pre-snap motion and shifts, with the running game often forgotten. There is much less of a focus on play action. The Martz variant favored an elusive feature back who can catch the ball, such as Hall of Famer Marshall Faulk, over the power runners the Turner scheme prefers. Martz credited both his influences on his variation of the offensive system and his overall coaching philosophy to Don Coryell. [28] Martz first learned the Air Coryell offense as an assistant coach working under his mentor, Ernie Zampese. [29] Martz continued learning the offense in the mid-90s as the quarterbacks coach of the Washington Redskins, working under the tutelage of head coach Norv Turner. [30]

In 1999, Martz, then serving as offensive coordinator for Hall of Fame head coach Dick Vermeil, helped pilot the St. Louis Rams to victory in Super Bowl XXXIV. [31] [32] The Rams' offense, which was also known as "The Greatest Show on Turf", featured Hall of Fame QB Kurt Warner, who was the NFL MVP for the 1999 season (Warner earned another NFL MVP award in 2001). RB Marshall Faulk also played a prominent role in the St. Louis offense that season. Faulk won the NFL MVP award in 2000, and he would also win 3 straight AP NFL Offensive of the Year awards from 1999-2001. Additionally, St. Louis's offensive line was strong, anchored by multiple-time Pro Bowler and fellow Hall of Famer Orlando Pace. Lastly, the Rams' receiving core was impressive, featuring 4 strong wide receivers: Hall of Fame WR Isaac Bruce, Torry Holt, Ricky Proehl and Az-Zahir Hakim. When Vermeil retired after Super Bowl XXXIV, Martz replaced him as head coach, starting in the 2000 season. The Rams set a new NFL record for total offensive yards that same season, with 7,335. 5,492 of those were passing yards, also a new NFL team record. From 1999-2001, St. Louis became the only team in NFL history to score 500+ points in 3 consecutive years. In all, the Rams totaled 1,569 points, more than any other NFL team in any 3-year stretch. The Rams also became the first team to gain more than 20,000 yards of total offense in a 3-year stretch. [33] Martz coached the Rams from 2000-2005, compiling a 53-32 regular season record and a 3-4 playoff record.

Meanwhile, Vermeil came out of retirement to coach the Kansas City Chiefs from 2001-2005. Despite having decent success in Kansas City, he wasn't able to lead the Chiefs to a Super Bowl appearance. However, in 2022, Vermeil earned induction into the Pro Football Hall of Fame for his work as an NFL head coach.

Al Saunders's version

Al Saunders was the former WR coach under Don Coryell in San Diego and succeeded him as head coach of the Chargers. The Al Saunders variant is heavily influenced by Coryell and Saunders's former boss, former Coryell assistant and 2-time Redskins coach Joe Gibbs, whose Ace formation (single back, 2 WRs, 1 TE, and 1 H back) was immensely effective in the 1980s. The Saunders variant is a more conservative variant than the Martz version, but also quite complex. It is better suited for a veteran QB. It does not insist on size at WR or HB like the Turner variant and as such has difficulties in short yardage and red zone situations. It does not require a pair of dominant fast WRs like the Martz system, and is not as aggressive attacking down the field. Consequently, the Saunders system does not score as many points as the Martz system. Saunders's scheme is a more sound variant than Martz's scheme, offering a little more blocking and more run support for the QB. The Saunders variant pulls in many Coryell concepts that the Turner system eliminated in favor of simplicity.

West Coast offense comparisons

The Coryell offense attacked vertically through seams, while the West Coast offense moved laterally as much as vertically through angles on curl and slant routes. [34] The Coryell offense had lower completion percentages than the West Coast offense, but the returns were greater on a successful play. "The Coryell offense required more talented players, a passer who could get the ball there, and men who can really run—a lot of them," said Walsh. [35] He said the West Coast offense was developed out of necessity to operate with less talented players. He noted, "[Coryell] already had the talent and used it brilliantly." [35]

Impact

Former head coach Marty Schottenheimer said "putting three receivers on one side and flooding that area" probably originated from the Coryell offense. [36] Head coach Bill Belichick notes that the pass-catching tight ends that get paid the most money are "all direct descendants of Kellen Winslow" and there are fewer tight ends now that can block on the line. [22] Former defensive coordinator Joe Collier credits the Coryell offense with creating an evolution by using multiple receivers, forcing defenses to counter with different packages. As a result, more defensive backs were drafted, and linebackers that could also cover inside receivers were sought. [37] Defenses were altered to use nickel and dime defenses in response to offensive formation; their usage was no longer limited to down and distance. [38] Former head coach Dick Vermeil said no other NFL offense "performs more efficiently or scores more points" than the Coryell offense. [39]

See also

Related Research Articles

<span class="mw-page-title-main">Los Angeles Chargers</span> National Football League franchise in Inglewood, California

The Los Angeles Chargers are a professional American football team based in the Los Angeles metropolitan area. The Chargers compete in the National Football League (NFL) as a member of the American Football Conference (AFC) West division, and play their home games at SoFi Stadium in Inglewood, California, which they share with the Los Angeles Rams.

<span class="mw-page-title-main">Wide receiver</span> Offensive position in American and Canadian football

A wide receiver (WR), also referred to as a wideout, historically known as a split end (SE) or flanker (FL), is an eligible receiver in gridiron football. A key skill position of the offense, WR gets its name from the player being split out "wide", farthest away from the rest of the offensive formation.

<span class="mw-page-title-main">Tight end</span> Position in American football

The tight end (TE) is a position in American football, arena football, and Canadian football, on the offense. The tight end is often a hybrid position with the characteristics and roles of both an offensive lineman and a wide receiver. Like offensive linemen, they are usually lined up on the offensive line and are large enough to be effective blockers. On the other hand, unlike offensive linemen, they are eligible receivers adept enough to warrant a defense's attention when running pass patterns.

In American football, the West Coast offense is an offense that places a greater emphasis on passing than on running.

<span class="mw-page-title-main">Dan Fouts</span> American football player and broadcaster (born 1951)

Daniel Francis Fouts is an American former football quarterback who played for the San Diego Chargers of the National Football League (NFL) throughout his 15-season career (1973-87). After a relatively undistinguished first five seasons in the league, Fouts came to prominence as the on-field leader during the Chargers' Air Coryell period. He led the league in passing every year from 1979 to 1982, passing for over 4,000 yards in the first three of these - no previous quarterback had posted consecutive 4,000-yard seasons. Fouts was voted a Pro Bowler six times, 1st-team All-Pro twice, and Offensive Player of the Year in 1982. He was named a member of the NFL 1980s All-Decade Team, and elected to the Pro Football Hall of Fame in 1993, his first year of eligibility.

<span class="mw-page-title-main">Kellen Winslow</span> American football player (born 1957)

Kellen Boswell Winslow Sr. is an American former professional football player in the National Football League (NFL). A member of the Pro Football Hall of Fame (1995), he is widely recognized as one of the greatest tight ends in the league's history. Winslow played his entire NFL career from 1979 to 1987 with the San Diego Chargers after being selected in the first round of the 1979 NFL Draft. He played college football for the University of Missouri, where he was a consensus All-American. He was also inducted into the College Football Hall of Fame (2002).

<span class="mw-page-title-main">Charlie Joiner</span> American football player and coach (born 1947)

Charles B. Joiner Jr. is an American former professional football player who was a wide receiver in the American Football League (AFL) and National Football League (NFL) for 18 seasons. He is best known for his career with the San Diego Chargers, with whom he spent 11 seasons. Before joining the Chargers, he played for the Houston Oilers and Cincinnati Bengals each for four seasons. He retired with the most career receptions, receiving yards, and games played of any wide receiver in NFL history. Joiner was inducted into the Pro Football Hall of Fame in 1996.

<span class="mw-page-title-main">I formation</span>

The I formation is one of the most common offensive formations in American football. The I formation draws its name from the vertical alignment of quarterback, fullback, and running back, particularly when contrasted with the same players' alignments in the T formation.

<span class="mw-page-title-main">Al Saunders</span> American football coach

Alan Keith Saunders is an American football coach who most recently served as the senior offensive assistant for the Cleveland Browns of the National Football League (NFL).

"The Greatest Show on Turf" was a nickname for the record-breaking offense of the St. Louis Rams during the 1999, 2000, and 2001 National Football League seasons. The offense was designed by attack-oriented offensive coordinator and head coach Mike Martz, who mixed an aerial attack and a run offense in an Air Coryell-style offense. The Rams' offense during these three seasons produced record scoring and yardage, three NFL MVP honors, and two Super Bowl appearances and one championship. In 2000, the team set an NFL record with 7,335 total offensive yards. Of those, 5,492 were passing yards, also an NFL team record.

An H-back is an offensive position in American football. The H-back lines up similarly to a tight end, but is "set back" from the line of scrimmage, and is thus counted as one of the four "backs" in the offensive formation. The H-back, while similar in name, should not be confused with "halfback" or "running back", which are used to denote a separate, primary ball-carrying backfield position. The position was made notable in the National Football League (NFL) by the Washington Redskins under head coach Joe Gibbs, who ran a two tight end system. The position was named F-back when used later in Norv Turner's offensive system. The position is similar to that of a slotback.

<span class="mw-page-title-main">Don Coryell</span> American football coach (1924–2010)

Donald David Coryell was an American football coach, who coached in the National Football League (NFL) first with the St. Louis Cardinals from 1973 to 1977 and then the San Diego Chargers from 1978 to 1986.

<span class="mw-page-title-main">Ron Turner (American football)</span> American football player and coach (born 1953)

Ronald David Turner is an American football coach and former player.

<span class="mw-page-title-main">Spread offense</span> Offensive scheme in American and Canadian football

The spread offense is an offensive scheme in gridiron football that typically places the quarterback in the shotgun formation, and "spreads" the defense horizontally using three-, four-, and even five-receiver sets. Used at every level of the game including professional, college, and high school programs across the US and Canada, spread offenses often employ a no-huddle approach. Some implementations of the spread also feature wide splits between the offensive linemen.

<span class="mw-page-title-main">Ken Zampese</span> American football coach (born 1967)

Kenneth Zampese is an American football coach who is the quarterbacks coach for the Washington Commanders of the National Football League (NFL). Zampese began his coaching career at his alma mater, the University of San Diego, and has held a variety of college and professional coaching positions.

The New England Patriots generally run a modified Erhardt-Perkins offensive system and a Fairbanks-Bullough 3–4 defensive system, though they have also used a 4–3 defense and increased their use of the nickel defense.

<span class="mw-page-title-main">San Diego Chargers</span> American football team history

The San Diego Chargers were a professional American football team that played in San Diego from 1961 until the end of the 2016 season, before relocating to Los Angeles, where the franchise had played its inaugural 1960 season. The team is now known as the Los Angeles Chargers.

<span class="mw-page-title-main">Pro-style offense</span> NFL-style American football offensive scheme

A pro-style offense in American football is any offensive scheme that resembles those predominantly used at the professional level of play in the National Football League (NFL), in contrast to those typically used at the collegiate or high school level. Pro-style offenses are fairly common at top-quality colleges but much less used at the high school level. The term should not be confused with a pro set, which is a specific formation that is used by some offenses at the professional level.

References

General

Specific

  1. "Football 101: Deep Shots with the Air Coryell Offense". Bleacher Report. March 8, 2012. Retrieved April 28, 2021.
  2. Team Records: Passing
  3. Jaworski 2010, pp.86, 95
  4. Jaworski 2010, pp.90,113
  5. Carroll, Bob; Gershman, Michael; Neft, David; Thorn, John (1999). Total Football: The Official Encyclopedia of the National Football League . HarperCollins Publishers. p. 1800. ISBN   9780062701749 . Retrieved June 6, 2022 via Internet Archive.
  6. 1 2 3 4 Jaworski 2010, p.80
  7. Jaworski 2010, pp.85–86
  8. Elderkin, Phil (September 16, 1980). "Chargers, in passing, write a book". Christian Science Monitor. Archived from the original on February 1, 2014.
  9. Paris, Jay (January 11, 2013). "Don Coryell's Hall bid falls short". U-T San Diego. Archived from the original on January 18, 2013.
  10. "Air Coryell". Pro Football Hall of Fame. Archived from the original on July 15, 2011.
  11. "Shannhan, Tom. 2008. "Don Coryell Belongs in the Hall of Fame", July 1 (accessed October 4, 2008)". Archived from the original on 2008-09-19. Retrieved 2012-06-18.
  12. 1 2 3 Jaworski 2010, p.87
  13. Jaworski 2010, p.108
  14. Jaworski 2010, pp.80–81
  15. Jaworski 2010, p.90
  16. Jaworski 2010, p.91
  17. NFL.com video feature on Air Coryell
  18. 1 2 Jaworski 2010, p.81
  19. 1 2 Jaworski 2010, p.92
  20. Jaworski 2010, p.93
  21. Jaworski 2010, pp.93–94
  22. 1 2 Jaworski 2010, p.112
  23. Jaworski 2010, pp.107–108
  24. 1 2 Jaworski 2010, p.110
  25. "Tight end rankings: Do Sharpe, Gonzalez deserve top spot?". USA Today. July 21, 2008. Retrieved April 30, 2010.
  26. Justice, Richard (October 9, 1997). "Heir Coryell". Washington Post. Retrieved April 29, 2021.
  27. Randall, Mike (January 15, 2014). "What Makes Norv Turner's Air Coryell System Go? (Part 1)". Baltimore Sports and Life. Retrieved April 28, 2021.
  28. "'The Greatest Show on Turf' started with Don Coryell". espn.com. February 6, 2016. Retrieved April 29, 2021.
  29. Kelly, Danny (July 17, 2014). "Don Coryell, the man who created the modern NFL". SBNation. Retrieved May 21, 2021.
  30. Howman, David (May 12, 2019). "Taking a deep dive into the Air Coryell scheme the Cowboys have traditionally used" . Retrieved May 21, 2021.
  31. "Revisiting the Greatest Show on Turf". September 23, 2014. Retrieved April 28, 2021.
  32. Baskin, Ben (May 23, 2017). "How Mike Martz and The Greatest Show on Turf kicked off an NFL Revolution". Sports Illustrated. Retrieved April 28, 2021.
  33. "Rams Offense Sets NFL Records". January 5, 2002. Retrieved April 28, 2021.
  34. Jaworski 2010, p.128
  35. 1 2 Jaworski 2010, p.129
  36. Jaworski 2010, p.111
  37. Jaworski 2010, p.113
  38. Jaworski 2010, p.101
  39. Jaworski 2010, p.114