Interactions in the Quaternary Systems H\\r sub/2sub\\r O–Er(NO\\r sub/3sub\\r )\\r sub/3sub\\r –La(NO\\r sub/3sub\\r )\\r sub/3sub\\r –Pr(NO\\r sub/3sub\\r )\\r sub/3sub\\r , H\\r sub/2sub\\r O–Er(NO\\r sub/3sub\\r )\\r sub/3sub\\r –La(NO\\r sub/3sub\\r )\\r sub/3sub\\r –Nd(NO\\r sub/3sub\\r )\\r sub/3sub\\r , and H\\r sub/2sub\\r O–Er(NO\\r sub/3sub\\r )\\r sub/3sub\\r –Pr(NO\\r sub/3sub\\r )\\r sub/3sub\\r –Nd(NO\\r sub/3sub\\r )\\r sub/3sub\\r to Very High Concentrations