A seal having a body portion, at least one lip portion extending from the body portion, and a protrusion formed on the at least one lip portion. Matrices Su are constructed for the successive values of u starting with S1=S, and, for u>1, each matrix Su is obtained by performing on the matrix Su\u22121, column permutations where appropriate, then linear manipulations involving the line of index u. Each of parts to be engaged 16b, 16b is formed at an open end of each mounting member 16.