In mathematics, an O*-algebra is an algebra of possibly unbounded operators defined on a dense subspace of a Hilbert space. The original examples were described by and , who studied some examples of O*-algebras, called Borchers algebras, arising from the Wightman axioms of quantum field theory. and began the systematic study of algebras of unbounded operators.
Hilbert spaces only have non-dense subspaces
( z1 have :ARG0 ( z2 space :name ( z3 name :op "Hilbert" ) ) :ARG1 ( z4 space :mod ( z5 dense :polarity - ) ) :mod ( z6 only ) )