Correction (×), ligne 13 : « δ Π = d Π d ξ δ ξ + d Π d η δ η + d Π d ζ δ ζ + d Π d ξ 1 δ ξ 1 + d Π d η 1 δ η 1 + d Π d ζ 1 δ ζ {\displaystyle \delta \Pi ={\frac {d\Pi }{d\xi }}\,\delta \xi +{\frac {d\Pi }{d\eta }}\,\delta \eta +{\frac {d\Pi }{d\zeta }}\,\delta \zeta +{\frac {d\Pi }{d\xi _{1}}}\,\delta \xi _{1}+{\frac {d\Pi }{d\eta _{1}}}\,\delta \eta _{1}+{\frac {d\Pi }{d\zeta _{1}}}\,\delta \zeta } » → « δ Π = d Π d ξ δ ξ + d Π d η δ η + d Π d ζ δ ζ + d Π d ξ 1 δ ξ 1 + d Π d η 1 δ η 1 + d Π d ζ 1 δ ζ 1 {\displaystyle \delta \Pi ={\frac {d\Pi }{d\xi }}\,\delta \xi +{\frac {d\Pi }{d\eta }}\,\delta \eta +{\frac {d\Pi }{d\zeta }}\,\delta \zeta +{\frac {d\Pi }{d\xi _{1}}}\,\delta \xi _{1}+{\frac {d\Pi }{d\eta _{1}}}\,\delta \eta _{1}+{\frac {d\Pi }{d\zeta _{1}}}\,\delta \zeta _{1}} » (coquille : ajout de l’indice 1 {\displaystyle _{1}} dans le dernier terme du second membre de l’équation.)