:: deftheorem defines is_SetOfSimpleGraphs_of SGRAPH1:def 6 :
for X, GG being set holds
( GG is_SetOfSimpleGraphs_of X iff ( SimpleGraphStruct(# {},({} (TWOELEMENTSETS {})) #) in GG & ( for V being Subset of X
for E being Subset of (TWOELEMENTSETS V)
for n being set
for Evn being finite Subset of (TWOELEMENTSETS (V \/ {n})) st SimpleGraphStruct(# V,E #) in GG & n in X & not n in V holds
SimpleGraphStruct(# (V \/ {n}),Evn #) in GG ) & ( for V being Subset of X
for E being Subset of (TWOELEMENTSETS V)
for v1, v2 being set st SimpleGraphStruct(# V,E #) in GG & v1 in V & v2 in V & v1 <> v2 & not {v1,v2} in E holds
ex v1v2 being finite Subset of (TWOELEMENTSETS V) st
( v1v2 = E \/ {{v1,v2}} & SimpleGraphStruct(# V,v1v2 #) in GG ) ) ) );