1. The problem statement, all variables and given/known data http://img171.imageshack.us/img171/5997/76283103.png [Broken] 3. The attempt at a solution I think a good place to start is with the definition of regular. My definition is: σ is regular if ∂σ/∂s and ∂σ/∂v are linearly independent. Want to confirm I'm on the right track before going further!