PropCheck.TargetedPBT.forall_targeted

You're seeing just the macro forall_targeted, go back to PropCheck.TargetedPBT module for more information.
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forall_targeted(arg, list)

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The forall_targeted macros uses the targeted PBT component of PropEr to try that all instances of xs fulfill property prop.

In contrast to exists, often the property here is negated.