Could someone please help me with this question

Prove Theorem 5.1.10. Let f: D - R and let c be an accumulation point of D . Then the following are equivalent: (a) f does not have a limit at c. > c is not in ( Sn) czlius. & ( sn ) but it is in The ser of (b) There exists a sequence (Sn) in D with each sn * c such that (Sn) converges to c, but (f(S,) ) is accum- not convergent in R . ulation points of ( s. ) 1. (a) = (b) If f does not have a limit at c then there exists a sequence (Sn) in D with each Sn # c such that (Sn) converges to c , but (f(Sn)) is not convergent in R. 2. (b) = (a) If there exists a sequence (Sn) in D with each sn # c such that (Sn) converges to c , but (f( Sn) ) is not convergent in R then f does not have a limit at c