:: deftheorem defines is_negative_alliance_in ROUGHS_3:def 6 :
for X being set
for R being Relation of X holds
( R is_negative_alliance_in X iff for x, y being object st x in X & y in X & ex z being object st
( z in X & [x,z] in R & not [z,y] in R ) holds
not [x,y] in R );