Overview

Last class:

• Rice’s theorem (meta reasoning is uncomputable)
• HALT was uncomputable
• Notempty was uncomputable

Today:

• Restrict model of computation
• Context-Free Grammars

Summary of TMs

• Defined TMs
• TMs can simulate all Python programs
• HOCEIT
• Church-Turing thesis
• Universality
• Uncomputability

If Turing Complete, any semantic property of that model is also uncomputable

Context Free Grammars

$G=(V,\Sigma, R,S)$

$V$: Variables

$\Sigma$: Alphabet terminals