b. 1945
Alasdair Urquhart is a Canadian logician and philosopher based at the University of Toronto, known for his foundational work on relevance logic and the computational complexity of propositional logics. His research bridges philosophical logic and theoretical computer science, with influential results on the difficulty of decision problems for non-classical logics.
Proved exponential lower bounds on proof length in relevance logic
Established key complexity results for decision problems in non-classical logics
Advanced the semantics of relevance and substructural logics
Contributed to understanding the computational limits of logical reasoning