  We propose a call-by-value lambda calculus extended with a new construct
inspired by abductive inference and motivated by the programming idioms of
machine learning. Although syntactically simple the abductive construct has a
complex and subtle operational semantics which we express using a style based
on the Geometry of Interaction. We show that the calculus is sound, in the
sense that well typed programs terminate normally. We also give a visual
implementation of the semantics which relies on additional garbage collection
rules, which we also prove sound.
