Description: The union of two (undirected) simple hypergraphs (with the same vertex
set) represented as ordered pair: If <. V , E >. and
<. V , F >. are simple hypergraphs, then <. V , E u. F >. is a
(not necessarily simple) hypergraph - the vertex set stays the same, but
the edges from both graphs are kept, possibly resulting in two edges
between two vertices. (Contributed by AV, 29-Nov-2020)(Revised by AV, 24-Oct-2021)