The Lazy Peregrin problem is the Arbre equivalent of the Travelling Salesman problem on Earth.
The problem concerns a wandering fraa who needs to visit several maths that are scattered randomly around the world. The fraa does not wish to work harder than he has to and so must find the shortest possible route that will take him to each of his destinations.
Fraa Orolo mentions this problem to Fraa Erasmas while they are together at the Temple of Orithena. The Lazy Peregrin problem is offered as an example of a problem that requires analyzing many possible solutions at once in order to find the best solution.
Before the Second Sack, Saunt Grod and forerunners of the Ita developed a machine that could solve such problems. Fraa Jad appears similarly capable of solving such problems using meditation and chanting as evidenced by his ability to solve the Teglon, another problem that requires evaluating many possible solutions at once.