for F, H being ZF-formula st H is disjunctive holds
( ( F = the_left_argument_of H implies ex G being ZF-formula st F 'or' G = H ) & ( ex G being ZF-formula st F 'or' G = H implies F = the_left_argument_of H ) & ( F = the_right_argument_of H implies ex G being ZF-formula st G 'or' F = H ) & ( ex G being ZF-formula st G 'or' F = H implies F = the_right_argument_of H ) )