let p, q be Element of CQC-WFF ; :: thesis: for x being bound_QC-variable holds
( Ex x,(p 'or' q) is valid iff (Ex x,p) 'or' (Ex x,q) is valid )
let x be bound_QC-variable; :: thesis: ( Ex x,(p 'or' q) is valid iff (Ex x,p) 'or' (Ex x,q) is valid )
(Ex x,(p 'or' q)) <=> ((Ex x,p) 'or' (Ex x,q)) is valid by Th45;
hence ( Ex x,(p 'or' q) is valid iff (Ex x,p) 'or' (Ex x,q) is valid ) by Lm15; :: thesis: verum