(98)Subject to Community and national law, undertakings, in particular mutual and mutual-type associations, should be able to form concentrations or groups, not through capital ties but through formalised strong and sustainable relationships, based on contractual or other material recognition that guarantees a financial solidarity between those undertakings. Where a dominant influence is exercised through a centralised coordination, those undertakings should be supervised in accordance with the same rules as those provided for groups constituted through capital ties in order to achieve an adequate level of protection for policy holders and a level playing field between groups.