let p, q be Element of CQC-WFF ; :: thesis: for x being bound_QC-variable holds
( Ex (x,(p => q)) is valid iff (All (x,p)) => (Ex (x,q)) is valid )
let x be bound_QC-variable; :: thesis: ( Ex (x,(p => q)) is valid iff (All (x,p)) => (Ex (x,q)) is valid )
(Ex (x,(p => q))) <=> ((All (x,p)) => (Ex (x,q))) is valid by Th66;
hence ( Ex (x,(p => q)) is valid iff (All (x,p)) => (Ex (x,q)) is valid ) by Lm15; :: thesis: verum