Introduction. -Theoretical Framework.- Theoretical Foundation for a Pattern Based Approach to Algebra.- Methodology.- Epistemological and Didactical Analyses of the Mathematics Potential in Tasks on Generalisation of Shape Patterns.- Constrained Feedback Potential in Adidactical Situations.- Complexity of Turning a Situation of Action into a Situation of Formulation.- Complexity of Operating in the Situation of Validation.- Synthesis.- References.- Appendices.¿