l -> FunDecl -> Either ([DerivationError], DerivDecl) ()
isDeclared der derF declF = when (not (isEq derF declF)) $ 
                                Left ([DerivedFunctionDeclaredNotEqual (derF ^. funDeclName)],der)


mkIndHyp :: Variable -> Relati
isDeclared :: DerivDecl -> FunDecl -> FunDecl -> Either ([DerivationError], DerivDecl) ()
isDeclared der derF declF = when (not (isEq derF declF)) $ 
                                Left ([DerivedFunctionDeclaredNotEqual (derF ^. funDeclName)],der)
isDeclared der derF declF = when (not (isEq derF declF)) $ 
                                Left ([DerivedFunctionDeclaredNotEqual (derF ^. funDeclName)],der)