The book "Oranges are not the only fruit" is a typical postmodern novel.
Postmodernism developed during the sixties and its main tenets are:
• it does no longer belong in the concept of truth, it puts therefore the question of authority into doubt
• it does no longer believe in the concept of a centre as it generally happened in all the previous generations.
If modernism (covers the first three decades of the XX Century) was still looking for a centre, for a point of reference and put the question and the research on art in the centre, postmodernism questioned all that and came to the conclusion that there is no longer a single centre because saying that there is no absolute true ALSO IMPLIES THAT THERE IS NO MEANING. there is no longer a centre, but many centers and therefore MEANING IS ALWAYS DIFFERED : THERE IS A CONTINUOUS SLIPPING OF MEANING BECAUSE MEANING IS NEVER STABLE. The concept is connected to the relationship between: signifier and signified (they derive from signify).

[Roland Barthes fa un' analisi sulla semiotica della moda, un comportamento mentale grazie al quale le persone aderiscono a dei comportamenti in cui riconoscono un' autorità.
Lyotard fu il padre del postmodernismo]

The position of the reader is the best one because it is the reader that gives sense of the possible meaning.
A perfectly example of the postmodernism is "Oranges are not the only fruit" that relies on a reconstruction of the Bible structure in a new context (con+text) and there is a lot of intertextuality.
Another example is David Lodge's "Nice work" (ottimo lavoro). There are two characters: a male (Vik, short form of victory) and a female (Robyn Penrose, name linked to Robin Hood, an idealist. The surname suggests she is a writer).