let X be set ; :: thesis: for x, y being object
for R being Relation of X st [x,y] in R holds
( x in X & y in X )
let x, y be object ; :: thesis: for R being Relation of X st [x,y] in R holds
( x in X & y in X )
let R be Relation of X; :: thesis: ( [x,y] in R implies ( x in X & y in X ) )
assume [x,y] in R ; :: thesis: ( x in X & y in X )
then ( x in dom R & y in rng R ) by XTUPLE_0:def 12, XTUPLE_0:def 13;
hence ( x in X & y in X ) ; :: thesis: verum