Declarations -> Declarations -> [ThmDecl] ->
                   EDeriv -> EDeriv' (DeclPos,FunDecl)
checkDerivation pops decls imDecls thms =
                either Left (checkDer pops decls imDecls thms) 

getVarInSpec :: Variable -> Sp
checkDerivation :: [Operator] -> Declarations -> Declarations -> [ThmDecl] ->
                   EDeriv -> EDeriv' (DeclPos,FunDecl)
checkDerivation pops decls imDecls thms =
                either Left (checkDer pops decls imDecls thms)
checkDerivation pops decls imDecls thms =
                either Left (checkDer pops decls imDecls thms)