“…The present paper continues research in implicit computational complexity as initiated by Simmons [33], Bellantoni and Cook [4], and Leivant [18], [19], [20], which have led to resource-free, purely functional characterisations of many complexity classes, such as fptime [4], [21], [23], [5], [28], flinspace [2], [20], [5], [28], NP and the polynomial-time hierarchy [3], the Kalmár-elementary functions [30] and fpspace [15], [31], the exponential time functions of linear growth [9], and the Grzegorczyk hierarchy at and above the linearspace level [5], [28], [16], [17], among many others. As well, implicit characterisations through higher type recursion have been given for the Kalmár-elementary functions [22], [15], [1], for polynomial space [24], and for fptime [6], [13].…”