Compactness and finiteness theorems for isospectral manifolds. R. Brooks; P. Petersen; P. Perry — 1992 Journal für die reine und angewandte Mathematik
The Laplace operator on hyperbolic three manifolds with cusps of non-maximal rank. R. Froese; P. Hislop; P. Perry — 1991 Inventiones mathematicae
On Cheeger's inequality. R. Brooks; P. Perry; Petersen V; P. — 1993 Commentarii mathematici Helvetici