Question: What Lyricist is known for collaborations on musicals such as "Rex" and "Fiddler on the Roof"? 

Context paragraphs:
Cannonball Adderley's Fiddler on the Roof: Cannonball Adderley's Fiddler on the Roof is an album by jazz saxophonist Cannonball Adderley released on the Capitol label featuring performances of material from the Broadway musical "Fiddler on the Roof" by Adderley with Nat Adderley, Charles Lloyd, Joe Zawinul, Sam Jones and Louis Hayes.

Sheldon Harnick: Sheldon Harnick (born April 30, 1924) is an American lyricist best known for his collaborations with composer Jerry Bock on musicals such as "Fiddler on the Roof".

Randal Bays: Randal Bays (born 1950) is a fiddler, guitarist and composer.  The American-born Irish-style fiddle and guitar player first gained international recognition through his recordings and performances with Co.  Clare fiddler Martin Hayes in the early 1990s.  He began playing music at the age of eight and was widely known as a fiddler in the U.S. long before recording with Hayes as guitar accompanist.  Born in Indiana in 1950, Bays relocated to the Pacific Northwest as a teenager and has made his home in Oregon and Washington since then.  His musical life included serious study of the classical guitar, prior to taking up Irish fiddling in the 1970s.  At the time, he lived in Portland, Oregon, and was strongly influenced by Co.  Cavan accordion player Michael Beglan, also fiddler Kevin Burke and guitarist Mícheál Ó Domhnaill.

Joseph Stein: Joseph Stein (May 30, 1912 – October 24, 2010) was an American playwright best known for writing the books for such musicals as "Fiddler on the Roof" and "Zorba".

Uca minax: Uca minax, commonly known as the red‐jointed fiddler crab or brackish-water fiddler crab, is a species of fiddler crab that is found in the United States from Massachusetts to the Gulf of Mexico.  It is one of the most common macroinvertebrates in salt marshes in these states.  It prefers areas of low salinity than other fiddler crabs, and can be found in great numbers along the banks of tidal streams, even at distances greater than 50 km from the sea.

REX 5000: The Franklin REX 5, (also known as the “Rex-Pro”, as the “Rex 5000”, and with cosmetic variation as the “Rex 5001”) was one of the Rex line of Personal Digital Assistants, each a PCMCIA PC card and thus the size of a credit card, built around a Toshiba microprocessor emulating a Zilog Z80.  The REX firmware was written by Starfish Software, and the hardware was manufactured by Citizen Electronics.  Earlier models in this line (the Rex and the Rex-3) had almost no input possibilities except to download data when installed in a host computer or in a docking station; the Rex 5 added a sixth button and introduced a modal input method.  (The later REX 6000 again had only five buttons, but included a touch screen.)  Further, with 512 KB of RAM, the Rex 5 had twice the memory of the Rex-3 (which, in turn, had four times that of the original Rex).

Concept musical: Concept musicals were first introduced in the 1940s, though two shows compete for the title of 'first concept musical:' "Allegro" and "Love Life".  The form began to flourish in the late 1960s, with the advent and subsequent popularity of "Man of La Mancha", "Cabaret", and "Hair".  Stephen Sondheim, the most prolific author of concept musicals, created "Company" in 1970, bringing the genre to the forefront of the commercial realm.  Director-choreographer Bob Fosse and producer-director Harold Prince were equally instrumental in making defining contributions to the concept musical.  Modern examples of the concept musical include "Assassins" and "Avenue Q".  Shows ranging from "Fiddler on the Roof" to "Sweeney Todd" have been argued as being concept musicals, though there is little critical agreement.

Fiddler crab: A fiddler crab, sometimes known as a "calling crab", may be any of approximately 100 species of semi-terrestrial marine crabs which make up the genus Uca.  As members of the family Ocypodidae, fiddler crabs are most closely related to the ghost crabs of the genus "Ocypode".  This entire group is composed of small crabs – the largest being slightly over two inches across.  Fiddler crabs are found along sea beaches and brackish inter-tidal mud flats, lagoons and swamps.  Fiddler crabs are most well known for their sexually dimorphic claws; the males’ major claw is much larger than the minor claw while the females’ claws are both the same size.

Rex (musical): Rex is a musical with music by Richard Rodgers, lyrics by Sheldon Harnick and libretto by Sherman Yellen, based on the life of King Henry VIII.  The original production starred Nicol Williamson.

Alexandra Silber: Alexandra Michelle Silber (born July 3, 1983) is an American actress, singer, writer and educator.  She has performed roles on Broadway, in London's West End, on television and film, and concert stages.  Among other stage roles, in London, she created the role of Laura Fairlie in "The Woman in White" (2005), played Hodel in "Fiddler on the Roof" (2007) and Julie Jordan in "Carousel" (2008).  In New York, she appeared in "Hello Again" (2010), "Master Class" (2011), created the role of Sara Jane in "Arlington" (2012–14) and as Tzeitel in the Broadway revival of "Fiddler on the Roof" (2015).

Supporting paragraphs: Rex (musical) Sheldon Harnick
Answer: Sheldon Harnick