Procrustes was a bandit in greek mythology, famous for inviting travelers to spend the night in his iron bed, where he will tie them up when they were asleep and sawed the body parts than didn't fit into his bed, so as to make them fit. You can see why I've named a stemming algorithm like that.
In a more serious way, this is a spanish stemming implementation, based on the paper "A Word Stemming Alrorithm for the Spanish Language" that you can see at http://www.cis.strath.ac.uk/cis/research/publications/papers/strath_cis_publication_2234.pdf.