let x be bound_QC-variable; :: thesis: for p being QC-formula st p is closed holds
Ex x,p is closed
let p be QC-formula; :: thesis: ( p is closed implies Ex x,p is closed )
assume still_not-bound_in p = {} ; :: according to QC_LANG1:def 30 :: thesis: Ex x,p is closed
then still_not-bound_in p c= {x} by XBOOLE_1:2;
hence Ex x,p is closed by Th32; :: thesis: verum