Contract for the sale of land – validity of notice to complete – whether contract required fourteen clear days notice – whether any shorter period permissible – whether purchasers repudiated the contract by failing to complete on an agreed date (where a valid notice to complete had not been served) – purchasers insisting on an erroneous interpretation of the contract as the basis of their refusal to complete on the agreed date – purchasers acting in good faith – failure of vendor to point out the precise error in the purchasers’ interpretation.