let H, F be Element of QC-WFF ; :: 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 QC_LANG1:def 22;
hence ( F is_immediate_constituent_of H iff F = the_argument_of H ) by Th60; :: thesis: verum