:: deftheorem Def1 defines lambda DIRAF:def 1 :
for X being non empty set
for R, b₃ being Relation of [:X,X:] holds
( b₃ = lambda R iff for a, b, c, d being Element of X holds
( [[a,b],[c,d]] in b₃ iff ( [[a,b],[c,d]] in R or [[a,b],[d,c]] in R ) ) );