  Applicative bisimilarity is a coinductive characterisation of observational
equivalence in call-by-name lambda-calculus, introduced by Abramsky (1990).
Howe (1996) gave a direct proof that it is a congruence, and generalised the
result to all languages complying with a suitable format. We propose a
categorical framework for specifying operational semantics, in which we prove
that (an abstract analogue of) applicative bisimilarity is automatically a
congruence. Example instances include standard applicative bisimilarity in
call-by-name, call-by-value, and call-by-name non-deterministic
$\lambda$-calculus, and more generally all languages complying with a variant
of Howe's format.
