expr_fvs (Let (NonRec bndr rhs) body) fv_cand in_scope acc
  = (rhs_fvs (bndr, rhs) `unionFV` addBndr bndr (expr_fvs body))
      fv_cand in_scope acc
expr_fvs (Let (NonRec bndr rhs) body) fv_cand in_scope acc
  = (rhs_fvs (bndr, rhs) `unionFV` addBndr bndr (expr_fvs body))
      fv_cand in_scope acc
expr_fvs (Let (NonRec bndr rhs) body) fv_cand in_scope acc
  = (rhs_fvs (bndr, rhs) `unionFV` addBndr bndr (expr_fvs body))
      fv_cand in_scope acc