“…More generally, mathematical finance and biology provide examples of elliptic differential operators which become degenerate along the boundary of a 'quadrant', R d−m × R m + , and R d−m ×R m + is a state space for the corresponding Markov process. Examples primarily motivated by mathematical finance include affine processes [1,14,17,22,23,24,40,41], which may be viewed as extensions of geometric Brownian motion (see, for example, [71]), the Heston stochastic volatility process [51], and the Wishart process [14,42,45,46,47]. Examples of this kind which arise in mathematical biology include the multi-dimensional Kimura diffusions and their local model processes [27,Equations (1.5) and (1.20)].…”