The example is based on the one in Using Reservoirs. Only three houses will be built, one of each type. We will compute a first solution to this problem while displaying some information about the modifications to the activities.
We will use the parameter traceLevel to set the type and amount of information returned. 
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If traceLevelis 0, then we want to trace all the modifications that pertain to the plumbing phase for each house.
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If traceLevelis 1, we want to know when the start variable of a set of activities is increased or becomes bound. The set of activities is defined as all those that require the fourth worker (that is, all the activities of type garden, painting or moving).
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If traceLevelis 2, we want to have the same type of information, but for all the activities in the problem.