let R be Relation; :: thesis: ( R is transitive iff for x, y, z being set st [x,y] in R & [y,z] in R holds
[x,z] in R )

hereby :: thesis: ( ( for x, y, z being set st [x,y] in R & [y,z] in R holds
[x,z] in R ) implies R is transitive )

assume R is transitive ; :: thesis: for x, y, z being set st [x,y] in R & [y,z] in R holds
[x,z] in R
then A1: R is_transitive_in field R by Def16;
let x, y, z be set ; :: thesis: ( [x,y] in R & [y,z] in R implies [x,z] in R )
assume that
A2: [x,y] in R and
A3: [y,z] in R ; :: thesis: [x,z] in R
A4: z in field R by A3, RELAT_1:15;
( x in field R & y in field R ) by A2, RELAT_1:15;
hence [x,z] in R by A1, A2, A3, A4, Def8; :: thesis: verum

end;

assume for x, y, z being set st [x,y] in R & [y,z] in R holds
[x,z] in R ; :: thesis: R is transitive
then for x, y, z being set st x in field R & y in field R & z in field R & [x,y] in R & [y,z] in R holds
[x,z] in R ;
then R is_transitive_in field R by Def8;
hence R is transitive by Def16; :: thesis: verum