I don't think 'cras es noster' is bad latin, as latinfag suggests in the Notable.

Nor would 'tomorrow thou art ours' be a proper translation – it is not nostri or nostrum, an objective or subjective genitive, but a nominative.

Tomorrow, 'thou' art 'we'. Singular is Plural. (There is an anomaly about the present vs. future tense, but I don't think that's a problem.)

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