How does Shakespeare Establish Theme, Character and Plot in Act One of "As You Like It"?

As in many of Shakespeare's comedies, the plot of As You Like It concerns lovers, and revolves around the overcoming of the obstacles to their love. After Act One, we have seen that Rosalind and Orlando are the central lovers of the play, and that Oliver and the Duke are the main impediments. As well as the theme of love, in Act One we see Shakespeare establishing the themes of jealousy and court versus country.
Strong characterisation is essential to the vitality of the plot. In Act One, we are introduced to a varied array of characters: Rosalind, Celia and Touchstone are witty and perceptive, Orlando is passionate and noble, and the Duke and Oliver are villainous and jealous.
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