The term SOLID is a popular acronym used to refer to a set of five principles of software architecture. These include: SRP (Single Responsibility), Open/Close, Liskov’s Substitution, Interface ...
Steenburgh, Thomas J. "The Invariant Proportion of Substitution (IPS) Property of Discrete-Choice Models." Harvard Business School Working Paper, No. 05-022, October 2004. (Revised June 2006.