The Court decided unanimously that the matter is justiciable, and that "prorogation will be unlawful if it has the effect of preventing parliament form being able to carry out its constitutional functions", and, that the "prolonged" suspension was "unusual", and that "the effects on the fundamentals of democracy was extreme".
"Hale says the court is “bound to conclude that the decision to advise her Majest to prorogue parliament was unlawful”."
IT IS UNLAWFUL!
(Fascinatingly, the Court's website is positively crawling along)
Possible outcomes, per David Allen Green:
Non-justiciable - government win
Justiciable but lawful - government win (though court may say "careful now")
Justiciable and declaration of unlawfulness - government defeat
Above, with coercive order and/or finding of improper motive - bad government defeat
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