Question: In between Clement Greenberg and Isabel Colegate who was a British author and literary agent?

Context paragraphs:
Isabel Colegate: Isabel Diana Colegate (born 10 September 1931) is a British author and literary agent.

Sidney Janis: Sidney Janis (July 8, 1896 – November 23, 1989) was a wealthy clothing manufacturer and art collector who opened an art gallery in New York in 1948.  His gallery quickly gained prominence, for he not only exhibited the work of most of the emerging leaders of Abstract Expressionism, but also that of such important European artists as Pierre Bonnard, Paul Klee, Joan Miró, and Piet Mondrian.  As the critic Clement Greenberg explained in a 1958 tribute to the dealer, Janis' exhibition practices had helped to establish the legitimacy of the Americans, for his policy "not only implied, it declared, that Jackson Pollock, Willem de Kooning, Franz Kline, Phillip Guston, Mark Rothko, and Robert Motherwell were to be judged by the same standards as Matisse and Picasso, without condescension, without making allowances."  Greenberg observed that in the late 1940s "the real issue was whether ambitious artists could live in this country by what they did ambitiously.  Sidney Janis helped as much as anyone to see that it was decided affirmatively."

Liana Burgess: Liana Burgess (born Liliana Macellari, September 25, 1929 – December 3, 2007) was an Italian translator and literary agent who was the second wife of English writer Anthony Burgess.  Burgess and Macellari had embarked on an affair while Burgess was married to his first wife, and Macellari gave birth to a son nine months after their meeting.  The couple became tax exiles in the late 1960s, living in Malta and Italy, and spent several years in the United States.  The couple finally settled in Monaco.  Macellari played an important role in Burgess's later literary career, negotiating film rights and acting as his European literary agent, and translating his novels.

Ira Silverberg: Ira Silverberg is an influential literary agent and editor in the New York publishing business.  Silverberg worked as a literary agent at Donadio & Ashworth, as Editor-in-Chief at Grove/Atlantic Press, and as editorial and publishing director at Serpent's Tail's U.S. projects, High Risk Books and Midnight Classics.  He also founded the marketing and public relations firm, Ira Silverberg Communications.  This firm has attracted clients like The Academy of American Poets, William S. Burroughs, the estate of David Wojnarowicz, Dennis Cooper, City Lights Publications, and Re/Search Publications.  He is currently an agent at Sterling Lord Literistic.

Marshall Plan (software): The Marshall Plan software is a novel writing software to assist in the technical aspects of novel writing.  The software automatically plots a novel based on literary agent Evan Marshall's novel writing system in his three book series, "The Marshall Plan for Novel Writing: A 16-Step Program Guaranteed to Take You From Idea to Completed Manuscript," "The Marshall Plan Workbook," and "The Marshall Plan for Getting Your Novel Published."  Marshall Plan software is published by Evan Marshall and Martha Jewett, literary agent and consultant.

Peter Buckman: Peter Buckman is an English writer and literary agent.  He has been involved in the publishing industry for many years; he was on the editorial board of Penguin Books, and a commissioning editor for the New American Library in New York City.  He has published novels, non fiction, a biography and short stories, and has also written for television and film, including an episode of Inspector Morse, three episodes of The House of Elliot and television movie The Tale of Sweeney Todd, which was directed by John Schlesinger.  He is currently a literary agent, having started The Ampersand Agency in 2003, notable for having discovered and represented Vikas Swarup, author of Q & A, which was filmed as Slumdog Millionaire, and also being the agent for the estate of prolific historical fiction writer Georgette Heyer.

The Shooting Party (novel): The Shooting Party is the ninth novel by Isabel Colegate published in 1980 that won the 1981 WH Smith Literary Award.  It was adapted into a 1985 film "The Shooting Party".  It is published as part of the Penguin Books Modern Classic series.

The Shooting Party: The Shooting Party is a 1985 British drama film directed by Alan Bridges and based on the book of the same name by Isabel Colegate.  The film is set in 1913 and shows the way of life of English aristocrats, gathered for pheasant shooting and general self-indulgence.  Their way of life is contrasted with the local rural poor, who serve as 'beaters', driving the game for the aristocrats to shoot.  It was entered into the 14th Moscow International Film Festival.

Clement Greenberg: Clement Greenberg ( ), occasionally writing under the pseudonym K. Hardesh (January 16, 1909 – May 7, 1994), was an American essayist known mainly as an influential visual art critic closely associated with American Modern art of the mid-20th century.  In particular, he is best remembered for his promotion of the abstract expressionist movement and was among the first published critics to praise the work of painter Jackson Pollock.

Helen Frankenthaler: Helen Frankenthaler (December 12, 1928 – December 27, 2011) was an American abstract expressionist painter.  She was a major contributor to the history of postwar American painting.  Having exhibited her work for over six decades (early 1950s until 2011), she spanned several generations of abstract painters while continuing to produce vital and ever-changing new work.  Frankenthaler began exhibiting her large-scale abstract expressionist paintings in contemporary museums and galleries in the early 1950s.  She was included in the 1964 "Post-Painterly Abstraction" exhibition curated by Clement Greenberg that introduced a newer generation of abstract painting that came to be known as Color Field.  Born in Manhattan, she was influenced by Greenberg, Hans Hofmann, and Jackson Pollock's paintings.  Her work has been the subject of several retrospective exhibitions, including a 1989 retrospective at the Museum of Modern Art in New York City, and been exhibited worldwide since the 1950s.  In 2001, she was awarded the National Medal of Arts.

Supporting paragraphs: Clement Greenberg Isabel Colegate
Answer: Isabel Diana Colegate