In each step of the clustering algorithm, the words from the triplets and the features are merged, if the overlap factor similarity measure (Curran, 2003) found them to be similar enough (over 80% overlapping words out of 200).
if the element (space, NASA, Mars) : (orbital, satellite, astronauts,...) and (space, launch, Mars) : (orbit, satellite, astronaut, ...) were found to be similar, they are merged to (space=2, NASA=1,Mars=1,launch=1) : (orbital=1,satellite=2,orbit=1,astronaut=1,...).