Question: What is a subtopic of a potential well that has the equation \phi: \nabla\phi = \vec{A}?
Paraphrase: What could be a subtopic of a potential well that has the condition phi: nablaphi = vec{A}?
SPARQL (Wikidata): SELECT ?answer WHERE { wd:Q761414 wdt:P1269 ?answer . ?answer wdt:P2534 ?x FILTER(contains(?x , '\phi: \nabla\phi = \vec{A}'))}