students a,b, C, courses: x, v,z, w (ay)2(an,)(b,x),(by),(b,w),(c,) R={(ay)2(a,w),(b,yx),(by),(b,w) RCAXB. ie.R is a subset ofAXB relation
students a,b,c, courses:x,y,z,w (a,y),(a,w),(b,x),(b,y),(b,w)，(c,w) R={(a,y),(a,w),(b,x),(b,y),(b,w)} RA×B, i.e. R is a subset of A×B relation
2.2 Binary relations Definition 2.5: let A and b be sets.A binary relation from A to B is a subset of AXB. A relation on a is a relation from a to A. If(a, bER, we say that a is related to b by Dy R, we also write a b. If (a,b)ER, we say that a is not related to b by R, we also write a u b. we say that empty set is an empty relation
2.2 Binary relations Definition 2.5: Let A and B be sets. A binary relation from A to B is a subset of A×B. A relation on A is a relation from A to A. If (a,b)R, we say that a is related to b by R, we also write a R b. If (a,b)R , we say that a is not related to b by R, we also write a ℟ b. we say that empty set is an empty relation