Our term "structure discovery" denotes the recovery of structure, such as the grouping of cells, that was intended by a spreadsheet's author but is not explicit in the spreadsheet. We are implementing structure discovery tools in the logic-programming language Prolog for our spreadsheet analysis program Model Master, by writing grammars for spreadsheet structures. The objective is an "intelligent structure monitor" to run beside Excel, allowing users to reconfigure spreadsheets to the representational needs of the task at hand. This could revolutionise spreadsheet "best practice". We also describe a formulation of spreadsheet reverse-engineering based on "arrows".