Comment on “Period function and normalizers of vector fields in Rn with n−1 first integrals” by D. Peralta-Salas [J. Differential Equations 244 (6) (2008) 1287–1303]

In a recent paper by D. Peralta-Salas in this journal (J. Differential Equations 244 (6) (2008) 1287–1303) there appears an incorrect result relating symmetries and first integrals of a vector field. The proof relies on a nonexistent theorem in a paper by Sherring and Prince (Trans. Amer. Math. Soc. 334 (1992) 433–453); the error is corrected in this comment.