3
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R[a_, b_] := FullSimplify[ KroneckerDelta[a, b] KroneckerDelta[a, b]]
R[a, b]
(* KroneckerDelta[a, b]^2 *)

Should the the full simplified answer not be just KroneckerDelta[a, b] due to idempotence?

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  • $\begingroup$ Failure to simplify isn't a bug - so I'd suggest changing the title of the question. $\endgroup$ – Jens Dec 31 '16 at 4:21
6
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Use PiecewiseExpand

R[a_, b_] := KroneckerDelta[a, b] KroneckerDelta[a, b] // PiecewiseExpand

R[a, b]

enter image description here

R[a_, b_] := Product[KroneckerDelta[a, b] , {n, 5}] // PiecewiseExpand

R[a, b]

enter image description here

R[a_, b_] := 
 Product[KroneckerDelta[a, b] , {n, m}] // PiecewiseExpand[#, m > 1] &

R[a, b]

enter image description here

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