# Chronology

### 1970 - 1980

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(1980 - 1990)

#### 1970

• Alan Baker is awarded a Fields Medal for his work on Diophantine equations.
• Matiyasevich shows that "Hilbert's tenth problem" is unsolvable, namely that there is no general method for determining when polynomial equations have a solution in whole numbers.

#### 1971

• Stephen Cook formulates the $P$ versus $NP$ problem regarding polynomial time algorithms.

#### 1972

• Thom publishes Structural Stability and Morphogenesis which explains catastrophe theory. The theory examines situations in which gradually changing forces lead to so-called catastrophes, or abrupt changes, and has important applications in biology and optics.
• Quillen formulates higher algebraic $K$-theory, a new tool that uses geometric and topological methods and ideas to formulate and solve major problems in algebra, particularly ring theory and module theory.

#### 1973

• Deligne proves the three "Weil conjectures".
• Chen Jingrun shows that every sufficiently large even integer is the sum of a prime and a number with at most two prime factors. It makes a major contribution to the Goldbach Conjecture.

#### 1975

• Feigenbaum discovers a new constant, approximately 4.669201609102..., which is related to period-doubling bifurcations and plays an important part in chaos theory.
• Mandelbrot publishes Les objets fractals, forme, hasard et dimension which describes the theory of fractals.

#### 1976

• Lakatos work Proofs and Refutations is published as a book two years after his death. First published in four parts in 1963-64 the work gives Lakatos's account of how mathematics develops.
• Thurston is awarded the Oswald Veblen Geometry Prize of the American Mathematical Society for his work on foliations.
• Appel and Haken show that the Four Colour Conjecture is true using 1200 hours of computer time to examine around 1500 configurations. (See this History Topic.)

#### 1977

• Adleman, Rivest, and Shamir introduce public-key codes, a system for passing secret messages using large primes and a key which can be published.

#### 1979

• Connes publishes work on non-commutative integration theory.