  We describe a method for merging multiple spreadsheets into one sheet, and/or
exchanging data among the sheets, by expressing each sheet's formulae as an
algebraic (equational) theory and each sheet's values as a model of its theory,
expressing the overlap between the sheets as theory and model morphisms, and
then performing colimit, lifting, and Kan-extension constructions from category
theory to compute a canonically universal integrated theory and model, which
can then be expressed as a spreadsheet. Our motivation is to find methods of
merging engineering models that do not require consensus (agreement) among the
authors of the models being merged, a condition fulfilled by our method because
theory and model morphisms are semantics-preserving. We describe a case study
of this methodology on a real-world oil and gas calculation at a major energy
company, describing the theories and models that arise when integrating two
different casing pressure test (MASP) calculation spreadsheets constructed by
two non-interacting engineers. We also describe the automated theorem proving
burden associated with both verifying the semantics preservation of the overlap
mappings as well as verifying the conservativity/consistency of the resulting
integrated sheet. We conclude with thoughts on how to apply the methodology to
scale engineering efforts across the enterprise.
