let p, q be Element of QC-WFF ; :: thesis: Free (p => q) = (Free p) \/ (Free q)
p => q = 'not' (p '&' ('not' q)) by QC_LANG2:def 2;
hence Free (p => q) = Free (p '&' ('not' q)) by Th50
.= (Free p) \/ (Free ('not' q)) by Th53
.= (Free p) \/ (Free q) by Th50 ;
:: thesis: verum