Dynamic Sets

Hello Gams - World,

i just started with modelling in Gams due to study reasons and came up with following problem. I want to model this PLSP lotsizing scheduling problem and have some issues with modelling with restriction 4.3
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. Here i don’t know how to model the dynamic set of delta, which size depends on sp(j). Neither do i know were to define sp(j)… as equation or parameter?
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I highly appreciate any help !!

Cheers