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1. A golf ball comprising:
an inner core layer comprising a thermoplastic highly-neutralized ionomer comprising a copolymer of ethylene and an α,β-unsaturated carboxylic acid, an organic acid or salt thereof, and sufficient cation source to neutralize the acid groups of the copolymer by 80% or greater, and having a geometric center hardness less than a surface hardness to define a first positive hardness gradient; an outer core layer disposed about the inner core, the outer core being formed from a homogenous thermoset composition and having an interior hardness less than an outer surface hardness to define a second positive hardness gradient; an inner cover layer disposed about outer core layer; and an outer cover layer disposed about the inner cover layer, wherein the first and second hardness gradients each have a slope and the slope of the second hardness gradient is less than the slope of the first hardness gradient such that a ratio of the first and second slopes is 0.8 to 0.85.
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