Axel Thue

Axel Thue (Norwegian: [tʉː]; 19 February 1863 – 7 March 1922), was a Norwegian mathematician, known for highly original work in diophantine approximation, and combinatorics.

He stated in 1914 the so-called word problem for semigroups or Thue problem, closely related to the halting problem.

His only known PhD student was Thoralf Skolem.

The esoteric programming language Thue is named after him.

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Thue (programming language)

Thue (/ˈtuːeɪ/ TOO-ay) is an esoteric programming language invented by John Colagioia in early 2000. It is a meta-language that can be used to define or recognize Type-0 languages from the Chomsky hierarchy. Because it is able to define languages of such complexity, it is also Turing-complete itself. Thue is based on a nondeterministic string rewriting system called semi-Thue grammar, which itself is named after the Norwegian mathematician Axel Thue; inspiration is also taken from the grue. The author describes it as follows: "Thue represents one of the simplest possible ways to construe constraint-based programming. It is to the constraint-based paradigm what languages like OISC are to the imperative paradigm; in other words, it's a tar pit."

Production rules

A Thue program starts with a rulebase, which is a series of substitution rules, each of this form:

The rulebase terminates with a lone production symbol on a line:

The initial state is a series of symbols which follow the rulebase.