let G be ext-real-membered set ; :: thesis: for g, f being ext-real number st g in G holds
g - f in G -- f
let g, f be ext-real number ; :: thesis: ( g in G implies g - f in G -- f )
f in {f} by TARSKI:def 1;
hence ( g in G implies g - f in G -- f ) by Th61; :: thesis: verum