English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

I N the July number of the BULLETIN Dr. Eisenhart treated these surfaces and reached the following conclusions : ' ' The ruled surfaces defined by the equations y + t*x = ^ I T 7 2 + Cxti + C, , , 1 3 _ ix v/1 + ^ = (^ + C, Vl + fJ 2 + C3) • % are the only surfaces whose first and second fundamental forms can be taken for the second and first fundamental forms of a surface. Further the second surface is only the first to a translation près. And of these surfaces the only real one is the sphere of radius uni ty." In fact the above equations represent the spheres of radius unity and nothing else. For we have y + *i + O + >/i + P) x=(e, + 1 )0 + s/T+J)+ c2 + c3 y — zi + {fi — \ / r + V ) x = (cx — 1 ) 0 — \/\ +/x 2 )+ c2 — c8 or

Concerning surfaces whose first and second fundamental forms are the second and first fundamental forms respectively of another surface