Fichera's existence principle

In mathematics, and particularly in functional analysis, Fichera's existence principle is an existence and uniqueness theorem for solution of functional equations, proved by Gaetano Fichera in 1954.^[1] More precisely, given a general vector space V and two linear maps from it onto two Banach spaces, the principle states necessary and sufficient conditions for a linear transformation between the two dual Banach spaces to be invertible for every vector in V.^[2]

See also

• Banach fixed-point theorem – Theorem about metric spaces
• Babuška–Lax–Milgram theorem – Mathematical theorem
• Lax–Milgram theorem – Mathematical toolsPages displaying short descriptions of redirect targets
• Lions–Lax–Milgram theorem – a result in functional analysis with applications in the study of partial differential equationsPages displaying wikidata descriptions as a fallback
• Surjection of Fréchet spaces – Characterization of surjectivity