English dramatist Caryl Churchill is turning 87 this September. In advance of that landmark, the Public Theater is presenting Glass. Kill. What If If Only. Imp., a quadruple bill of Churchill one-acts new to New York. Like Albee on this side of the Atlantic, Churchill has always had a penchant for depicting humanity in rather abstract terms. Directed by Churchill specialist James Macdonald, these shorts are supplemented with entr’acte circus feats by a juggler (Maddox Morfit-Tighe) and an acrobat (Junru Wang). The evening’s fare may seem, at first blush, a random assortment but, upon reflection, common themes emerge.