The last decades have seen an explosive growth in biosciences, and astonishing progress in the mathematical modelling of fields as diverse as neurobiology, membrane formation, biomechanics, embryology, etc. (see e.g. J.  Murray,1990). The sequencing of biomolecules produces such a vast wealth of data on proteins and polynucleotides that the mere handling of the stored information becomes a computational challenge, let alone the analysis of phylogenetic trees and functional networks which is the main task of bioinformatics...