Add simplification to Rewriter to normalize lets:  let p1 = (let p2 = e2 in e1) in e3 --> let p2 = e2 in let p1 = e2 in e3 This means that unfolding p2 does not duplicate let p2 = ...
Add simplification to Rewriter to normalize lets:
 let p1 = (let p2 = e2 in e1) in e3 --> let p2 = e2 in let p1 = e2 in e3
This means that unfolding p2 does not duplicate let p2 = ...


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