Ordering is an important activity for cognitive development
of a child and it has a fruitful form in the idea of (finite) sequence. A
schematic representation of concrete sequences (of numbers or letters) is used
to foster the idea of function. Leading pupils to discover simple laws of
correspondence and to compose the expressions which formulate them seems to be
the first possible instance of such activities feasible in elementary school
Keywords: Sequences, discovering of rules, finding sums.