let A be QC-alphabet ; :: thesis: for F, H being Element of QC-WFF A st H is negative holds
( F is_immediate_constituent_of H iff F = the_argument_of H )
let F, H be Element of QC-WFF A; :: 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 24;
hence ( F is_immediate_constituent_of H iff F = the_argument_of H ) by Th43; :: thesis: verum