  We describe a general method to identify exact, local parent Hamiltonians for
trial states like quantum Hall or spin liquid states, which we have used
extensively during the past decade. It can be used to identify exact parent
Hamiltonians, either directly or via the construction of simpler annihilation
operators from which a parent Hamiltonian respecting all the required
symmetries can be constructed. Most remarkably, however, the method provides
approximate parent Hamiltonians whenever an exact solution is not available
within the space of presumed interaction terms.
