GAP vs. PAG

We propose a parametrized version of arity gap. The parametrized arity gap gap(f, ℓ) of a function f: Aⁿ → B measures the minimum decrease in the number of essential variables of f when ℓ consecutive identifications of pairs of essential variables are performed. We determine gap(f, ℓ) for an arbitrary function f and a positive integer ℓ. We also propose other variants of arity gap and discuss further problems pertaining to the effect of identification of variables on the number of essential variables of functions.