Computing with Bohm trees
This paper develops a general technique to analyze the head reduction of a term in a context. This technique is used to give a direct proof of the theorem of Hyland and Wadsworth : two lambda -terms that have the same Bohm trees, up to (possibly infinite) eta -equivalence, are operationally equivalent. It is also used to prove a conjecture of R. Kerth : Every unsolvable lambda -term has a decoration. This syntactical result is motivated by (and gives the solution to) a semantical problem.
bohm trees head reduction operational equivalence decoration lambda-calculus