Let A={a1,a2,a3,a4,a5} and B={b1,b2,b3,b4,} where ai's and bi's are school going students . Define a relation from A to B by xRy iff y is a true friend of x . If R={(a1,b1),(a2,b1),(a3,b3),(a4,b2},(a5,b2)} . Prove that R is neither one one nor onto
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Solution
Since (a1,b1),(a2,b1) are present in R, it means b1 is related to both a1 and a2. This means it is many one since many are related to one in the co domain. since the range of R consists of only {b1,b2,b3} and since codomain has b4 and b4 more, it means R is not onto but into.