prov:value
| - h the proviso that _ _ (a) when A is a group of the formula 1_ wherein there is no nitrogen at either position a or position b , Z 3 is 0 , S or CH_ ; R 4 is hydrogen or C. -C, alkyl; Z 4 is (CH- ) , wherein p is 1 1 6 1 p 2 or 2, or S; Y is CH 2 , C=0, 0, or S, and Y is CH???, 0 or S, with the proviso that only one of Y 1 and Y2 can be CH_; (b) when A is a group of the formula _1 wherein there- i
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