Where-provenance for bidirectional editing in spreadsheets

We explore the idea of adding bidirectionality to spreadsheet formulas, so that editing the output can directly affect the input. We introduce the portal: a value paired with its where-provenance, that is, one or more links to its origin. When a portal is the result of a formula in a cell, that cell inherits the capability to edit locations described by the provenance. The simplicity of portals makes them amenable to implementation in existing systems. We analyse the list of functions provided by a widely used commercial spreadsheet and find that many frequently used functions work with portals with no modification.