let F, H be ZF-formula; :: thesis: ( H is negative implies ( F is_immediate_constituent_of H iff F = the_argument_of H ) )
assume H is negative ; :: thesis: ( F is_immediate_constituent_of H iff F = the_argument_of H )
then H = 'not' (the_argument_of H) by Def30;
hence ( F is_immediate_constituent_of H iff F = the_argument_of H ) by Th52; :: thesis: verum