# Step-Indexed Biorthogonality: a Tutorial Example (Abstract)

The purpose of this note is to illustrate the use of step-indexing
combined with biorthogonality to construct syntactical logical
relations. It walks through the details of a syntactically simple,
yet non-trivial example: a proof of the "CIU Theorem'' for
contextual equivalence in the untyped call-by-value
λ-calculus with recursively defined functions.