By Tetsuo Ida, Mircea Marin, and Taro Suzuki, from EUROCAST 2001, available from the SCORE website:

This paper introduces a higher-order lazy narrowing calculus (HOLN for short) that solves higher-order equations over the domain of simply typed λ-terms. HOLN is an extension and refinement of Prehofer’s higher-order narrowing calculus LN using the techniques developed in the refinement of a first-order lazy narrowing calculus LNC. HOLN is defined to deal with both unoriented and oriented equations. It keeps track of the variables which are to be bound to normalized answers. We discuss the operating principle of HOLN, its main properties, i.e. soundness and completeness, and its further refinements. The solving capability of HOLN is illustrated with an example of program calculation.