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16 votes
2 answers
3k views

Why is there no product type in simply typed lambda-calculus?

$\DeclareMathOperator\Pair{Pair}\DeclareMathOperator\First{First}\DeclareMathOperator\Second{Second}\DeclareMathOperator\Left{Left}\DeclareMathOperator\Right{Right}\DeclareMathOperator\Choice{Choice}$...
winitzki's user avatar
  • 271
8 votes
1 answer
321 views

Is every total computable function definable by a normalizing lambda term?

$\newcommand{\nat}{\mathbb{N}}$ $\newcommand{\then}{\ \Longrightarrow\ }$ A partial function $f : \mathbb{N} \to \mathbb{N}$ is said to be $\lambda$-definable if there is a term $F \in \Lambda$ such ...
Andrew Polonsky's user avatar
8 votes
0 answers
155 views

Is every total computable function definable by a strongly total lambda term?

Every computable (total) function $f : \mathbb{N} \to \mathbb{N}$ is definable in untyped pure lambda calculus in the sense that there is a term $F$ such that, for every Church's numeral $c_n = \...
Valery Isaev's user avatar
  • 4,459
3 votes
1 answer
404 views

Is there an easy decision algorithm for the inhabitation problem for simple types?

Consider the basic system of simple types usually known as $TA_\lambda$. One can prove that (as a consequence of the Subject Reduction Property and the fact that any typable term is strongly $\beta$-...
Alfie's user avatar
  • 31
1 vote
1 answer
169 views

Interaction-based approximation for HP-complete λ-theory?

We are looking for a proof or counter-examples for the following hypothesis. Two combinators $M$ and $N$ are solvable and equivalent in the HP-complete sensible $\lambda$-theory iff either $$ \exists ...
Anton Salikhmetov's user avatar