Flesh: Currently, lookup_var returns a reference to the value of a var. When a unop is called, this has the effect of negating the value in the table. Thus:

    $zip = 1
    foo::xmin = -$zip
    foo::xmax =  $zip

This results in both xmin and xmax being set to the same value (-1). The fix is to have lookup_var return a copy rather than a reference.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2829/piraha-lookup-ref-issue