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φ 0 := d x 123 + d x 145 + d x 167 + d x 246 − d x 257 − d x 347 − d x 356 {\displaystyle \varphi _{0}:=\mathrm {d} x^{123}+\mathrm {d} x^{145}+\mathrm {d} x^{167}+\mathrm {d} x^{246}-\mathrm {d} x^{257}-\mathrm {d} x^{347}-\mathrm {d} x^{356}}