 # is left-extensional (right-extensional) according to ⊩ if it is left-extensional (respectively, right-extensional) in its ith position for each i (1 ≤ i ≤ n), and finally # is extensional according to ⊩ when # is both left- and right-extensional according to ⊩. For n = 1 we drop the subscript, the above conditions reducing to (LE) and (RE):