//Creating array for permutation infos for current bijection.
// permutationInfos[i] = new ArrayList<>();
//Iterating through stretches of indices
for (Stretch stretch : new StretchIteratorS(diffIds))
if (stretch.length == 1) { //Indices with unique index id (stretch.length == 1) [Non permutable indices].
//Corresponding contraction in from tensor
long fromIndexContraction = fromContractions[seedFromIndex][diffIdsPermutation[stretch.from]];
//Corresponding contraction in target tensor
long targetIndexContraction = targetContractions[seedTargetIndex][diffIdsPermutation[stretch.from]];