Abstract
Numerical design and planning problems can often be formulated conveniently as a set of equations constraining the values of related variables, i.e., as a numerical or more generally as an interval constraint satisfaction problem (ICSP). However, due to theoretical and practical problems, no tools for solving ICSPs properly in the general case have thus far been designed and implemented. The authors discuss both theoretical and practical problems of solving ICSPs, and present solution approaches taken in the new interval constraint satisfaction tool INC++. The tool can be applied, for example, as the basis for next generation interval constraint spreadsheets.