Dear Members: can someone help me with a taxonomic question. I am trying to distinguish between fixed characters and polymorphic characters. I think the question can be stated: Given a matrix of x rows (objects = specimens) and y columns (attributes = fixed and polymorphic characters) with each attribute having 1-few discrete states, which attributes are needed to place all objects in groups such that each group is defined by a unique combination of attribute states and no group has 2 or more states of any attribute? Thanks. Sincerely. Andrew Henderson