let X, Y be set ; :: thesis: for f being PartFunc of X,Y
for g being Function st g in TotFuncs f holds
f tolerates g

let f be PartFunc of X,Y; :: thesis: for g being Function st g in TotFuncs f holds
f tolerates g

let g be Function; :: thesis: ( g in TotFuncs f implies f tolerates g )
assume g in TotFuncs f ; :: thesis: f tolerates g
then ex g' being PartFunc of X,Y st
( g' = g & g' is total & f tolerates g' ) by Def7;
hence f tolerates g ; :: thesis: verum