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Formal Aspects of Computer
Science – Week 12
RECAP
Lee McCluskey, room 2/07
Email [email protected]
Logic
• Used in theoretical computer science, language
semantics and artificial intelligence
• Many types of logics – depends on the application
• Logic languages tend to be very expressive,
declarative, equipped with methods of reasoning
Prolog
• A PROGRAMMING LANGUAGE modelled on first
order logic
• No statement sequencing, assignment, iteration,
overwrite-able variables in the traditional sense
• Instead – matching, recursion, 1 data type (the
term), simple syntax, backtracking
Reasoning with Logic
• First Order Logic syntactically well formed sentences
are called wffs.
• Reasoning in Logic is about proving that some wff
wff1 logically follows from another wff wff2.
• There are many SOUND laws of inference in Logic
which help us do reasoning.
Resolution
• Prolog is in a form of logic called “Clausal Form”. Every
Prolog Clause has at least one positive literal. Prolog allows
some “extra” and “meta” logical predicates, but its execution
is based on the inference rule of Resolution.
• Resolution is a sound law of inference in FOL. When used in
a Resolution Refutation method, using a fair search method,
it is also complete.
• Application: we looked at how logic can be used as a formal
specification language.