  We prove an orbifold conjecture for a solvable automorphism group. Namely, we
show that if V is a C_2-cofinite simple vertex operator algebra and G is a
finite solvable automorphism group of V, then the fixed point vertex operator
subalgebra V^G is also C_2-cofinite. This offers a mathematically rigorous
background to orbifold theories of finite type with solvable automorphism
groups.
