let p be Element of CQC-WFF ; :: thesis: for x being Element of bound_QC-variables holds p is_subformula_of All (x,p)
let x be Element of bound_QC-variables ; :: thesis: p is_subformula_of All (x,p)
p is_proper_subformula_of All (x,p) by QC_LANG2:71;
hence p is_subformula_of All (x,p) by QC_LANG2:def 21; :: thesis: verum