		model
		{
		   for (i in 1:ns){
			  nbiops[i]    <- sum(biopsies[i, ])  
		      true[i]       ~ dcat(p[])
		      biopsies[i, 1:4]  ~ dmulti(error[true[i], ], nbiops[i])
		   }
		   error[2,1:2] ~ ddirch(prior[1:2])
		   error[3,1:3] ~ ddirch(prior[1:3])
		   error[4,1:4] ~ ddirch(prior[1:4])
		   p[1:4]       ~ ddirch(prior[]);     # prior for p
		}