SetSails! is an eLearning application with which students learn to transform terms in set algebra. There are several different exercises in which one has to proof the correctness of an equivalence. In each step one first selects a rule (e.g. commutative law) and then chooses a term that should be the result of applying that rule. In order not to make the solution obvious, distractors are included in the options. One distinctive feature of SetSails! is that the learner is not forced to transform the equivalence ”from left to right”; he or she can also use the opposite way. It is even possible to do transformations in both directions in parallel, as can be seen in the screenshot. The user may resort to several types of assistance that SetSails! offers. The set that is defined by a term is highlighted in a Venn diagram(external link). One can look up the rules of set algebra in a virtual book. While solving the exercise, the learner can at any time seek feedback on his previous transformation steps. This feedback helps him to discover mistakes on his own (e.g. wrong transformations or incorrect reasons), but also to to identify unnecessarily complex solutions (e.g. containing circular reasoning).