The present paper furnishes
some combinatorial preliminaries towards a study of natural transformations between
tensor products of shape functors ∧α and co-shape functors ∨α. The main
result is the construction of an explicit basis for the module defined by (1)
below; an apparently new result used for this purpose, which may be of some
independent interest, is a ‘column-free’ expression for the Young idempotent
NPN (in Young’s terminology) associated with a partition, given by 1.2
below.