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Published online by Cambridge University Press:ย 20 November 2018
Motivated by a question of Per Enflo, we develop a hypercube criterion for locating linear isometric copies of $\ell _{1}^{\left( n \right)}$ in an arbitrary real normed space $X$.
The said criterion involves finding ${{2}^{n}}$ points in $X$ that satisfy one metric equality. This contrasts nicely to the standard classical criterion wherein one seeks $n$ points that satisfy ${{2}^{n-1}}$ metric equalities.