
theorem
for X, Y being set st X c= Y holds CompleteSGraph X c= CompleteSGraph Y
proof
 let X, Y be set such that
A1: X c= Y;
 let a be object;
 assume a in CompleteSGraph X;
 then consider V being finite Subset of X such that
 A2: a = V and
 A3: card V <= 2;
 V is Subset of Y by A1,XBOOLE_1:1;
 hence a in CompleteSGraph Y by A2,A3;
end;
