| http://www.w3.org/ns/prov#value | - However, another retainer serving the same functions as slots 18 a, 18 b may be substituted therefor for one of the two of left and right slots 18 a, 18 b, including structures so formed to retain grate-ends 4 a, 4 b (shown in FIG. 3A) from upward movement and movement away from the opposite retainer, and to permit rotation of grate-ends 4 a, 4 b about transverse axis 7.
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