“…In this case equivalence between the norms ∥v∥ H 1 (Ω) and ∥rot v∥ L 2 (Ω) under some conditions (see Theorem A.1 in [31], Lemma 2 in [49]) is on the base and in this way many problems are studied (cf. [1,6,12,13,[23][24][25]29,31,32,49,58,59]). In Section 1 of [29], the bilinear form (1.5) instead of (1.7) is used since two bilinear forms (1.5) and (1.7) for polygon or polyhedral domain under some boundary conditions are equal (cf.…”